diff --git a/.gitignore b/.gitignore
index c935546b..f3904c4c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,7 @@ vendor/
 data/schema.graphql
 composer.lock
 .idea
+docker-compose.yml
+Dockerfile
+docker/
+.env.local
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 83fdde7d..a97635d3 100644
--- a/composer.json
+++ b/composer.json
@@ -1,6 +1,6 @@
 {
   "name": "youshido/graphql",
-  "description": "Pure PHP GraphQL",
+  "description": "Pure PHP 8.1+ GraphQL",
   "license": "MIT",
   "authors": [
     {
@@ -10,15 +10,19 @@
     {
       "name": "Portey Vasil",
       "email": "portey@gmail.com"
+    },
+    {
+      "name": "Tom Atom",
+      "email": "tom@tomatom.com"
     }
   ],
   "require": {
-    "php": ">=5.5",
-    "ext-mbstring": "*",
-    "symfony/property-access": "^2.8 || ^3.4 || ^4.4"
+    "php": ">=8.1",
+    "symfony/property-access": "6.4.* || 7.4.*",
+    "ext-mbstring": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^4.8"
+    "phpunit/phpunit": "^10"
   },
   "autoload": {
     "psr-4": {
@@ -30,4 +34,4 @@
       "Youshido\\Tests\\": "tests"
     }
   }
-}
+}
\ No newline at end of file
diff --git a/examples/02_blog/Schema/BannerType.php b/examples/02_blog/Schema/BannerType.php
index a2b5db57..7d4c0bdb 100644
--- a/examples/02_blog/Schema/BannerType.php
+++ b/examples/02_blog/Schema/BannerType.php
@@ -5,13 +5,14 @@
 
 namespace Examples\Blog\Schema;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\StringType;
 
 class BannerType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config
             ->addField('title', new NonNullType(new StringType()))
@@ -19,7 +20,7 @@ public function build($config)
             ->addField('imageLink', new StringType());
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new ContentBlockInterface()];
     }
diff --git a/examples/02_blog/Schema/ContentBlockInterface.php b/examples/02_blog/Schema/ContentBlockInterface.php
index 7f62f6df..344c4223 100644
--- a/examples/02_blog/Schema/ContentBlockInterface.php
+++ b/examples/02_blog/Schema/ContentBlockInterface.php
@@ -6,6 +6,7 @@
 namespace Examples\Blog\Schema;
 
 
+use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Scalar\StringType;
@@ -13,7 +14,7 @@
 class ContentBlockInterface extends AbstractInterfaceType
 {
 
-    public function build($config)
+    public function build(InterfaceTypeConfig $config)
     {
         $config->addField('title', new NonNullType(new StringType()));
         $config->addField('summary', new StringType());
diff --git a/examples/02_blog/Schema/ContentBlockUnion.php b/examples/02_blog/Schema/ContentBlockUnion.php
index 17d4ba16..c0901991 100644
--- a/examples/02_blog/Schema/ContentBlockUnion.php
+++ b/examples/02_blog/Schema/ContentBlockUnion.php
@@ -6,16 +6,17 @@
 namespace Examples\Blog\Schema;
 
 
+use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\Union\AbstractUnionType;
 
 class ContentBlockUnion extends AbstractUnionType
 {
-    public function getTypes()
+    public function getTypes(): array
     {
         return [new PostType(), new BannerType()];
     }
 
-    public function resolveType($object)
+    public function resolveType(object $object): ?AbstractType
     {
         return empty($object['id']) ? null : (strpos($object['id'], 'post') !== false ? new PostType() : new BannerType());
     }
diff --git a/examples/02_blog/Schema/LikePostField.php b/examples/02_blog/Schema/LikePostField.php
index bf795fa4..d2d9d775 100644
--- a/examples/02_blog/Schema/LikePostField.php
+++ b/examples/02_blog/Schema/LikePostField.php
@@ -31,7 +31,7 @@ public function getType()
         return new PostType();
     }
 
-    public function build(FieldConfig $config)
+    public function build(FieldConfig $config): void
     {
         $config->addArgument('id', new NonNullType(new IntType()));
     }
diff --git a/examples/02_blog/Schema/PostStatus.php b/examples/02_blog/Schema/PostStatus.php
index b9f22aec..9450c7c4 100644
--- a/examples/02_blog/Schema/PostStatus.php
+++ b/examples/02_blog/Schema/PostStatus.php
@@ -10,7 +10,7 @@
 
 class PostStatus extends AbstractEnumType
 {
-    public function getValues()
+    public function getValues(): array
     {
         return [
             [
diff --git a/examples/02_blog/Schema/PostType.php b/examples/02_blog/Schema/PostType.php
index 030cf72b..7f20daf8 100644
--- a/examples/02_blog/Schema/PostType.php
+++ b/examples/02_blog/Schema/PostType.php
@@ -5,6 +5,7 @@
 
 namespace Examples\Blog\Schema;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\BooleanType;
@@ -14,10 +15,10 @@
 class PostType extends AbstractObjectType
 {
     /**
-     * @param \Youshido\GraphQL\Config\Object\ObjectTypeConfig $config
+     * @param ObjectTypeConfig $config
      * @throws \Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config
             ->addField('oldTitle', [
@@ -49,7 +50,7 @@ public function getOne($id)
         return DataProvider::getPost($id);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new ContentBlockInterface()];
     }
diff --git a/examples/03_relay_star_wars/Schema/FactionType.php b/examples/03_relay_star_wars/Schema/FactionType.php
index 77e0ec6f..72e04c9e 100644
--- a/examples/03_relay_star_wars/Schema/FactionType.php
+++ b/examples/03_relay_star_wars/Schema/FactionType.php
@@ -9,6 +9,7 @@
 namespace Examples\StarWars;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Relay\Connection\ArrayConnection;
 use Youshido\GraphQL\Relay\Connection\Connection;
 use Youshido\GraphQL\Relay\Field\GlobalIdField;
@@ -22,7 +23,7 @@ class FactionType extends AbstractObjectType
 
     const TYPE_KEY = 'faction';
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config
             ->addField(new GlobalIdField(self::TYPE_KEY))
@@ -49,7 +50,7 @@ public function build($config)
 
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'A faction in the Star Wars saga';
     }
@@ -59,7 +60,7 @@ public function getOne($id)
         return TestDataProvider::getFaction($id);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new NodeInterfaceType()];
     }
diff --git a/examples/03_relay_star_wars/Schema/ShipType.php b/examples/03_relay_star_wars/Schema/ShipType.php
index f43de101..dbc2777c 100644
--- a/examples/03_relay_star_wars/Schema/ShipType.php
+++ b/examples/03_relay_star_wars/Schema/ShipType.php
@@ -9,6 +9,7 @@
 namespace Examples\StarWars;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Relay\Field\GlobalIdField;
 use Youshido\GraphQL\Relay\NodeInterfaceType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
@@ -18,7 +19,7 @@ class ShipType extends AbstractObjectType
 {
     const TYPE_KEY = 'ship';
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config
             ->addField(new GlobalIdField(self::TYPE_KEY))
@@ -30,12 +31,12 @@ public function getOne($id)
         return TestDataProvider::getShip($id);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'A ship in the Star Wars saga';
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new NodeInterfaceType()];
     }
diff --git a/examples/03_relay_star_wars/Schema/StarWarsRelaySchema.php b/examples/03_relay_star_wars/Schema/StarWarsRelaySchema.php
index af73ae78..76293a0a 100644
--- a/examples/03_relay_star_wars/Schema/StarWarsRelaySchema.php
+++ b/examples/03_relay_star_wars/Schema/StarWarsRelaySchema.php
@@ -3,6 +3,7 @@
 namespace Examples\StarWars;
 
 use Youshido\GraphQL\Config\Schema\SchemaConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\InputField;
 use Youshido\GraphQl\Relay\Connection\ArrayConnection;
 use Youshido\GraphQL\Relay\Connection\Connection;
@@ -16,20 +17,19 @@
 
 class StarWarsRelaySchema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(SchemaConfig $config): void
     {
         $fetcher = new CallableFetcher(
             function ($type, $id) {
-                switch ($type) {
-                    case FactionType::TYPE_KEY:
-                        return TestDataProvider::getFaction($id);
+                return match ($type) {
+                    FactionType::TYPE_KEY => TestDataProvider::getFaction($id),
+                    ShipType::TYPE_KEY => TestDataProvider::getShip($id),
+                    default => null,
+                };
 
-                    case
-                    ShipType::TYPE_KEY:
-                        return TestDataProvider::getShip($id);
-                }
-
-                return null;
             },
             function ($object) {
                 return $object && array_key_exists('ships', $object) ? new FactionType() : new ShipType();
@@ -57,7 +57,7 @@ function ($object) {
                            'type' => new ListType(new StringType())
                        ]
                    ],
-                   'resolve' => function ($value = null, $args, $info) {
+                   'resolve' => function ($args, $info, $value = null) {
                        return TestDataProvider::getByNames($args['names']);
                    }
                ]);
diff --git a/examples/04_bookstore/Schema/Type/AuthorType.php b/examples/04_bookstore/Schema/Type/AuthorType.php
index ed377d86..983405b9 100644
--- a/examples/04_bookstore/Schema/Type/AuthorType.php
+++ b/examples/04_bookstore/Schema/Type/AuthorType.php
@@ -8,6 +8,7 @@
 
 namespace Examples\BookStore\Schema\Type;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\IdType;
@@ -15,7 +16,7 @@
 
 class AuthorType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config->addFields([
             'id'        => new NonNullType(new IdType()),
diff --git a/examples/04_bookstore/Schema/Type/BookType.php b/examples/04_bookstore/Schema/Type/BookType.php
index 80991d55..3eba22fc 100644
--- a/examples/04_bookstore/Schema/Type/BookType.php
+++ b/examples/04_bookstore/Schema/Type/BookType.php
@@ -17,7 +17,7 @@
 
 class BookType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config->addFields([
             'id'     => new IdType(),
diff --git a/examples/04_bookstore/Schema/Type/CategoryType.php b/examples/04_bookstore/Schema/Type/CategoryType.php
index c24da239..ed0e39ef 100644
--- a/examples/04_bookstore/Schema/Type/CategoryType.php
+++ b/examples/04_bookstore/Schema/Type/CategoryType.php
@@ -9,6 +9,7 @@
 namespace Examples\BookStore\Schema\Type;
 
 use Examples\BookStore\Schema\Field\CategoriesField;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\ListType\ListType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\IdType;
@@ -16,7 +17,7 @@
 
 class CategoryType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config)
     {
         $config->addFields([
             'id'      => new IdType(),
diff --git a/src/Config/AbstractConfig.php b/src/Config/AbstractConfig.php
index 55b3bf1d..67980dc3 100644
--- a/src/Config/AbstractConfig.php
+++ b/src/Config/AbstractConfig.php
@@ -9,8 +9,8 @@
 namespace Youshido\GraphQL\Config;
 
 
+use Exception;
 use Youshido\GraphQL\Exception\ConfigurationException;
-use Youshido\GraphQL\Exception\ValidationException;
 use Youshido\GraphQL\Validator\ConfigValidator\ConfigValidator;
 
 /**
@@ -20,42 +20,38 @@
  */
 abstract class AbstractConfig
 {
+    protected array $data;
 
-    /**
-     * @var array
-     */
-    protected $data = [];
+    protected mixed $contextObject;
 
-    protected $contextObject;
+    protected bool $finalClass = false;
 
-    protected $finalClass = false;
-
-    protected $extraFieldsAllowed = null;
+    protected bool $extraFieldsAllowed = false;
 
     /**
      * TypeConfig constructor.
      *
-     * @param array $configData
-     * @param mixed $contextObject
-     * @param bool  $finalClass
+     * @param mixed|null $contextObject
      *
      * @throws ConfigurationException
-     * @throws ValidationException
      */
-    public function __construct(array $configData, $contextObject = null, $finalClass = false)
+    public function __construct(array $configData, mixed $contextObject = null, bool $finalClass = false)
     {
-        if (empty($configData)) {
+        if ($configData === []) {
             throw new ConfigurationException('Config for Type should be an array');
         }
 
         $this->contextObject = $contextObject;
-        $this->data          = $configData;
-        $this->finalClass    = $finalClass;
+        $this->data = $configData;
+        $this->finalClass = $finalClass;
 
         $this->build();
     }
 
-    public function validate()
+    /**
+     * @throws ConfigurationException
+     */
+    public function validate(): void
     {
         $validator = ConfigValidator::getInstance();
 
@@ -64,7 +60,7 @@ public function validate()
         }
     }
 
-    public function getContextRules()
+    public function getContextRules(): array
     {
         $rules = $this->getRules();
         if ($this->finalClass) {
@@ -90,7 +86,7 @@ public function getType()
         return $this->get('type');
     }
 
-    public function getData()
+    public function getData(): array
     {
         return $this->data;
     }
@@ -100,23 +96,19 @@ public function getContextObject()
         return $this->contextObject;
     }
 
-    public function isFinalClass()
+    public function isFinalClass(): bool
     {
         return $this->finalClass;
     }
 
-    public function isExtraFieldsAllowed()
+    public function isExtraFieldsAllowed(): bool
     {
         return $this->extraFieldsAllowed;
     }
 
-
-    /**
-     * @return null|callable
-     */
-    public function getResolveFunction()
+    public function getResolveFunction(): ?callable
     {
-        return $this->get('resolve', null);
+        return $this->get('resolve');
     }
 
     protected function build()
@@ -125,44 +117,44 @@ protected function build()
 
     /**
      * @param      $key
-     * @param null $defaultValue
      *
      * @return mixed|null|callable
      */
-    public function get($key, $defaultValue = null)
+    public function get($key, $defaultValue = null): mixed
     {
         return $this->has($key) ? $this->data[$key] : $defaultValue;
     }
 
-    public function set($key, $value)
+    public function set($key, $value): static
     {
         $this->data[$key] = $value;
 
         return $this;
     }
 
-    public function has($key)
+    public function has($key): bool
     {
         return array_key_exists($key, $this->data);
     }
 
-    public function __call($method, $arguments)
+    /**
+     * @throws Exception
+     */
+    public function __call(string $method, array $arguments)
     {
-        if (substr($method, 0, 3) == 'get') {
+        if (str_starts_with($method, 'get')) {
             $propertyName = lcfirst(substr($method, 3));
-        } elseif (substr($method, 0, 3) == 'set') {
+        } elseif (str_starts_with($method, 'set')) {
             $propertyName = lcfirst(substr($method, 3));
             $this->set($propertyName, $arguments[0]);
 
             return $this;
-        } elseif (substr($method, 0, 2) == 'is') {
+        } elseif (str_starts_with($method, 'is')) {
             $propertyName = lcfirst(substr($method, 2));
         } else {
-            throw new \Exception('Call to undefined method ' . $method);
+            throw new Exception('Call to undefined method ' . $method);
         }
 
         return $this->get($propertyName);
     }
-
-
-}
+}
\ No newline at end of file
diff --git a/src/Config/Directive/DirectiveConfig.php b/src/Config/Directive/DirectiveConfig.php
index 2a148d83..e67ad919 100644
--- a/src/Config/Directive/DirectiveConfig.php
+++ b/src/Config/Directive/DirectiveConfig.php
@@ -24,13 +24,13 @@ class DirectiveConfig extends AbstractConfig
 
     protected $locations = [];
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'final' => true],
+            'name' => ['type' => TypeService::TYPE_STRING, 'final' => true],
             'description' => ['type' => TypeService::TYPE_STRING],
-            'args'        => ['type' => TypeService::TYPE_ARRAY],
-            'locations'   => ['type' => TypeService::TYPE_ARRAY],
+            'args' => ['type' => TypeService::TYPE_ARRAY],
+            'locations' => ['type' => TypeService::TYPE_ARRAY],
         ];
     }
 
@@ -39,7 +39,7 @@ public function getLocations()
         return $this->locations;
     }
 
-    public function build()
+    protected function build()
     {
         $this->buildArguments();
 
diff --git a/src/Config/Field/FieldConfig.php b/src/Config/Field/FieldConfig.php
index f1058730..ba946995 100644
--- a/src/Config/Field/FieldConfig.php
+++ b/src/Config/Field/FieldConfig.php
@@ -25,17 +25,17 @@ class FieldConfig extends AbstractConfig
 
     use ArgumentsAwareConfigTrait;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'              => ['type' => TypeService::TYPE_STRING, 'final' => true],
-            'type'              => ['type' => TypeService::TYPE_GRAPHQL_TYPE, 'final' => true],
-            'args'              => ['type' => TypeService::TYPE_ARRAY],
-            'description'       => ['type' => TypeService::TYPE_STRING],
-            'resolve'           => ['type' => TypeService::TYPE_CALLABLE],
-            'isDeprecated'      => ['type' => TypeService::TYPE_BOOLEAN],
+            'name' => ['type' => TypeService::TYPE_STRING, 'final' => true],
+            'type' => ['type' => TypeService::TYPE_GRAPHQL_TYPE, 'final' => true],
+            'args' => ['type' => TypeService::TYPE_ARRAY],
+            'description' => ['type' => TypeService::TYPE_STRING],
+            'resolve' => ['type' => TypeService::TYPE_CALLABLE],
+            'isDeprecated' => ['type' => TypeService::TYPE_BOOLEAN],
             'deprecationReason' => ['type' => TypeService::TYPE_STRING],
-            'cost'              => ['type' => TypeService::TYPE_ANY]
+            'cost' => ['type' => TypeService::TYPE_ANY]
         ];
     }
 
diff --git a/src/Config/Field/InputFieldConfig.php b/src/Config/Field/InputFieldConfig.php
index e0300698..846a3aa7 100644
--- a/src/Config/Field/InputFieldConfig.php
+++ b/src/Config/Field/InputFieldConfig.php
@@ -20,19 +20,19 @@
 class InputFieldConfig extends AbstractConfig
 {
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'              => ['type' => TypeService::TYPE_STRING, 'final' => true],
-            'type'              => ['type' => TypeService::TYPE_ANY_INPUT, 'final' => true],
-            'defaultValue'      => ['type' => TypeService::TYPE_ANY],
-            'description'       => ['type' => TypeService::TYPE_STRING],
-            'isDeprecated'      => ['type' => TypeService::TYPE_BOOLEAN],
+            'name' => ['type' => TypeService::TYPE_STRING, 'final' => true],
+            'type' => ['type' => TypeService::TYPE_ANY_INPUT, 'final' => true],
+            'defaultValue' => ['type' => TypeService::TYPE_ANY],
+            'description' => ['type' => TypeService::TYPE_STRING],
+            'isDeprecated' => ['type' => TypeService::TYPE_BOOLEAN],
             'deprecationReason' => ['type' => TypeService::TYPE_STRING],
         ];
     }
 
-    public function getDefaultValue()
+    public function getDefaultValue(): mixed
     {
         return $this->get('defaultValue');
     }
diff --git a/src/Config/Object/EnumTypeConfig.php b/src/Config/Object/EnumTypeConfig.php
index b7ea9b49..a8ce0d67 100644
--- a/src/Config/Object/EnumTypeConfig.php
+++ b/src/Config/Object/EnumTypeConfig.php
@@ -17,18 +17,19 @@
 
 class EnumTypeConfig extends AbstractConfig implements TypeConfigInterface
 {
-    use FieldsAwareConfigTrait, ArgumentsAwareConfigTrait;
+    use FieldsAwareConfigTrait;
+    use ArgumentsAwareConfigTrait;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'final' => true],
+            'name' => ['type' => TypeService::TYPE_STRING, 'final' => true],
             'description' => ['type' => TypeService::TYPE_STRING],
-            'values'      => ['type' => TypeService::TYPE_ENUM_VALUES, 'required' => true],
+            'values' => ['type' => TypeService::TYPE_ENUM_VALUES, 'required' => true],
         ];
     }
 
-    public function getValues()
+    public function getValues(): mixed
     {
         return $this->get('values', []);
     }
diff --git a/src/Config/Object/InputObjectTypeConfig.php b/src/Config/Object/InputObjectTypeConfig.php
index 2d2b2e0d..d2252b8d 100644
--- a/src/Config/Object/InputObjectTypeConfig.php
+++ b/src/Config/Object/InputObjectTypeConfig.php
@@ -13,11 +13,11 @@
 
 class InputObjectTypeConfig extends ObjectTypeConfig
 {
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'required' => true],
-            'fields'      => ['type' => TypeService::TYPE_ARRAY_OF_INPUT_FIELDS, 'final' => true],
+            'name' => ['type' => TypeService::TYPE_STRING, 'required' => true],
+            'fields' => ['type' => TypeService::TYPE_ARRAY_OF_INPUT_FIELDS, 'final' => true],
             'description' => ['type' => TypeService::TYPE_STRING],
         ];
     }
diff --git a/src/Config/Object/InterfaceTypeConfig.php b/src/Config/Object/InterfaceTypeConfig.php
index 01a27118..86fcecff 100644
--- a/src/Config/Object/InterfaceTypeConfig.php
+++ b/src/Config/Object/InterfaceTypeConfig.php
@@ -23,23 +23,30 @@
  */
 class InterfaceTypeConfig extends AbstractConfig implements TypeConfigInterface
 {
-    use FieldsAwareConfigTrait, ArgumentsAwareConfigTrait;
+    use FieldsAwareConfigTrait;
+    use ArgumentsAwareConfigTrait;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'final' => true],
-            'fields'      => ['type' => TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG, 'final' => true],
+            'name' => ['type' => TypeService::TYPE_STRING, 'final' => true],
+            'fields' => ['type' => TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG, 'final' => true],
             'description' => ['type' => TypeService::TYPE_STRING],
             'resolveType' => ['type' => TypeService::TYPE_CALLABLE, 'final' => true],
         ];
     }
 
+    /**
+     * @throws ConfigurationException
+     */
     protected function build()
     {
         $this->buildFields();
     }
 
+    /**
+     * @throws ConfigurationException
+     */
     public function resolveType($object)
     {
         $callable = $this->get('resolveType');
diff --git a/src/Config/Object/ListTypeConfig.php b/src/Config/Object/ListTypeConfig.php
index 02a82b09..82dd6c7f 100644
--- a/src/Config/Object/ListTypeConfig.php
+++ b/src/Config/Object/ListTypeConfig.php
@@ -13,12 +13,12 @@
 
 class ListTypeConfig extends ObjectTypeConfig
 {
-    public function getRules()
+    public function getRules(): array
     {
         return [
             'itemType' => ['type' => TypeService::TYPE_GRAPHQL_TYPE, 'final' => true],
-            'resolve'  => ['type' => TypeService::TYPE_CALLABLE],
-            'args'     => ['type' => TypeService::TYPE_ARRAY_OF_INPUT_FIELDS],
+            'resolve' => ['type' => TypeService::TYPE_CALLABLE],
+            'args' => ['type' => TypeService::TYPE_ARRAY_OF_INPUT_FIELDS],
         ];
     }
 
diff --git a/src/Config/Object/ObjectTypeConfig.php b/src/Config/Object/ObjectTypeConfig.php
index 76c57cdd..eea6e633 100644
--- a/src/Config/Object/ObjectTypeConfig.php
+++ b/src/Config/Object/ObjectTypeConfig.php
@@ -11,6 +11,7 @@
 use Youshido\GraphQL\Config\AbstractConfig;
 use Youshido\GraphQL\Config\Traits\FieldsAwareConfigTrait;
 use Youshido\GraphQL\Config\TypeConfigInterface;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
 use Youshido\GraphQL\Type\TypeService;
 
@@ -25,17 +26,20 @@ class ObjectTypeConfig extends AbstractConfig implements TypeConfigInterface
 
     use FieldsAwareConfigTrait;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'required' => true],
+            'name' => ['type' => TypeService::TYPE_STRING, 'required' => true],
             'description' => ['type' => TypeService::TYPE_STRING],
-            'fields'      => ['type' => TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG, 'final' => true],
-            'interfaces'  => ['type' => TypeService::TYPE_ARRAY_OF_INTERFACES]
+            'fields' => ['type' => TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG, 'final' => true],
+            'interfaces' => ['type' => TypeService::TYPE_ARRAY_OF_INTERFACES]
         ];
     }
 
-    protected function build()
+    /**
+     * @throws ConfigurationException
+     */
+    protected function build(): void
     {
         $this->buildFields();
     }
@@ -43,9 +47,8 @@ protected function build()
     /**
      * @return AbstractInterfaceType[]
      */
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return $this->get('interfaces', []);
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Config/Object/UnionTypeConfig.php b/src/Config/Object/UnionTypeConfig.php
index 35611cdd..ad9d3059 100644
--- a/src/Config/Object/UnionTypeConfig.php
+++ b/src/Config/Object/UnionTypeConfig.php
@@ -17,13 +17,14 @@
 
 class UnionTypeConfig extends AbstractConfig implements TypeConfigInterface
 {
-    use FieldsAwareConfigTrait, ArgumentsAwareConfigTrait;
+    use FieldsAwareConfigTrait;
+    use ArgumentsAwareConfigTrait;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'name'        => ['type' => TypeService::TYPE_STRING, 'required' => true],
-            'types'       => ['type' => TypeService::TYPE_ARRAY_OF_OBJECT_TYPES],
+            'name' => ['type' => TypeService::TYPE_STRING, 'required' => true],
+            'types' => ['type' => TypeService::TYPE_ARRAY_OF_OBJECT_TYPES],
             'description' => ['type' => TypeService::TYPE_STRING],
             'resolveType' => ['type' => TypeService::TYPE_CALLABLE, 'final' => true]
         ];
diff --git a/src/Config/Schema/SchemaConfig.php b/src/Config/Schema/SchemaConfig.php
index a34ad27b..65a4b65f 100644
--- a/src/Config/Schema/SchemaConfig.php
+++ b/src/Config/Schema/SchemaConfig.php
@@ -19,16 +19,14 @@
 class SchemaConfig extends AbstractConfig
 {
 
-    /**
-     * @var SchemaTypesList
-     */
-    private $typesList;
+    private readonly SchemaTypesList $typesList;
+
     /**
      * @var SchemaDirectivesList;
      */
-    private $directiveList;
+    private readonly SchemaDirectivesList $directiveList;
 
-    public function __construct(array $configData, $contextObject = null, $finalClass = false)
+    public function __construct(array $configData, mixed $contextObject = null, bool $finalClass = false)
     {
         $this->typesList = new SchemaTypesList();
         $this->directiveList = new SchemaDirectivesList();
@@ -36,14 +34,14 @@ public function __construct(array $configData, $contextObject = null, $finalClas
     }
 
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
-            'query'      => ['type' => TypeService::TYPE_OBJECT_TYPE, 'required' => true],
-            'mutation'   => ['type' => TypeService::TYPE_OBJECT_TYPE],
-            'types'      => ['type' => TypeService::TYPE_ARRAY],
+            'query' => ['type' => TypeService::TYPE_OBJECT_TYPE, 'required' => true],
+            'mutation' => ['type' => TypeService::TYPE_OBJECT_TYPE],
+            'types' => ['type' => TypeService::TYPE_ARRAY],
             'directives' => ['type' => TypeService::TYPE_ARRAY],
-            'name'       => ['type' => TypeService::TYPE_STRING],
+            'name' => ['type' => TypeService::TYPE_STRING],
         ];
     }
 
@@ -53,6 +51,7 @@ protected function build()
         if (!empty($this->data['types'])) {
             $this->typesList->addTypes($this->data['types']);
         }
+
         if (!empty($this->data['directives'])) {
             $this->directiveList->addDirectives($this->data['directives']);
         }
@@ -69,10 +68,8 @@ public function getQuery()
 
     /**
      * @param $query AbstractObjectType
-     *
-     * @return SchemaConfig
      */
-    public function setQuery($query)
+    public function setQuery($query): static
     {
         $this->data['query'] = $query;
 
@@ -82,34 +79,32 @@ public function setQuery($query)
     /**
      * @return ObjectType
      */
-    public function getMutation()
+    public function getMutation(): mixed
     {
         return $this->get('mutation');
     }
 
     /**
      * @param $query AbstractObjectType
-     *
-     * @return SchemaConfig
      */
-    public function setMutation($query)
+    public function setMutation($query): static
     {
         $this->data['mutation'] = $query;
 
         return $this;
     }
 
-    public function getName()
+    public function getName(): mixed
     {
         return $this->get('name', 'RootSchema');
     }
 
-    public function getTypesList()
+    public function getTypesList(): SchemaTypesList
     {
         return $this->typesList;
     }
 
-    public function getDirectiveList()
+    public function getDirectiveList(): SchemaDirectivesList
     {
         return $this->directiveList;
     }
diff --git a/src/Config/Traits/ArgumentsAwareConfigTrait.php b/src/Config/Traits/ArgumentsAwareConfigTrait.php
index 67703b95..8f16891d 100644
--- a/src/Config/Traits/ArgumentsAwareConfigTrait.php
+++ b/src/Config/Traits/ArgumentsAwareConfigTrait.php
@@ -9,14 +9,16 @@
 namespace Youshido\GraphQL\Config\Traits;
 
 
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\InputField;
 
 trait ArgumentsAwareConfigTrait
 {
-    protected $arguments = [];
+    protected array $arguments = [];
+
     protected $_isArgumentsBuilt;
 
-    public function buildArguments()
+    public function buildArguments(): void
     {
         if ($this->_isArgumentsBuilt) {
             return;
@@ -25,15 +27,15 @@ public function buildArguments()
         if (!empty($this->data['args'])) {
             $this->addArguments($this->data['args']);
         }
+
         $this->_isArgumentsBuilt = true;
     }
 
-    public function addArguments($argsList)
+    public function addArguments($argsList): static
     {
         foreach ($argsList as $argumentName => $argumentInfo) {
             if ($argumentInfo instanceof InputField) {
                 $this->arguments[$argumentInfo->getName()] = $argumentInfo;
-                continue;
             } else {
                 $this->addArgument($argumentName, $this->buildConfig($argumentName, $argumentInfo));
             }
@@ -42,17 +44,21 @@ public function addArguments($argsList)
         return $this;
     }
 
-    public function addArgument($argument, $argumentInfo = null)
+    /**
+     * @throws ConfigurationException
+     */
+    public function addArgument($argument, $argumentInfo = null): static
     {
         if (!($argument instanceof InputField)) {
             $argument = new InputField($this->buildConfig($argument, $argumentInfo));
         }
+
         $this->arguments[$argument->getName()] = $argument;
 
         return $this;
     }
 
-    protected function buildConfig($name, $info = null)
+    protected function buildConfig($name, $info = null): array
     {
         if (!is_array($info)) {
             return [
@@ -60,6 +66,7 @@ protected function buildConfig($name, $info = null)
                 'name' => $name
             ];
         }
+
         if (empty($info['name'])) {
             $info['name'] = $name;
         }
@@ -69,25 +76,21 @@ protected function buildConfig($name, $info = null)
 
     /**
      * @param $name
-     *
-     * @return InputField
      */
-    public function getArgument($name)
+    public function getArgument($name): ?InputField
     {
         return $this->hasArgument($name) ? $this->arguments[$name] : null;
     }
 
     /**
      * @param $name
-     *
-     * @return bool
      */
-    public function hasArgument($name)
+    public function hasArgument($name): bool
     {
         return array_key_exists($name, $this->arguments);
     }
 
-    public function hasArguments()
+    public function hasArguments(): bool
     {
         return !empty($this->arguments);
     }
@@ -95,12 +98,12 @@ public function hasArguments()
     /**
      * @return InputField[]
      */
-    public function getArguments()
+    public function getArguments(): array
     {
         return $this->arguments;
     }
 
-    public function removeArgument($name)
+    public function removeArgument($name): static
     {
         if ($this->hasArgument($name)) {
             unset($this->arguments[$name]);
diff --git a/src/Config/Traits/ConfigAwareTrait.php b/src/Config/Traits/ConfigAwareTrait.php
index a3b91305..04e34bdc 100644
--- a/src/Config/Traits/ConfigAwareTrait.php
+++ b/src/Config/Traits/ConfigAwareTrait.php
@@ -19,9 +19,10 @@ trait ConfigAwareTrait
 
     /** @var AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig */
     protected $config;
+
     protected $configCache = [];
 
-    public function getConfig()
+    public function getConfig(): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->config;
     }
@@ -31,13 +32,13 @@ protected function getConfigValue($key, $defaultValue = null)
         if (array_key_exists($key, $this->configCache)) {
             return $this->configCache[$key];
         }
-        $this->configCache[$key] = !empty($this->config) ? $this->config->get($key, $defaultValue) : $defaultValue;
+
+        $this->configCache[$key] = empty($this->config) ? $defaultValue : $this->config->get($key, $defaultValue);
         return $this->configCache[$key];
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return $this->getConfigValue('description');
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Config/Traits/DirectivesAwareConfigTrait.php b/src/Config/Traits/DirectivesAwareConfigTrait.php
index 1b7632b9..43e3963d 100644
--- a/src/Config/Traits/DirectivesAwareConfigTrait.php
+++ b/src/Config/Traits/DirectivesAwareConfigTrait.php
@@ -13,10 +13,11 @@
 
 trait DirectivesAwareConfigTrait
 {
-    protected $directives = [];
-    protected $_isDirectivesBuilt;
+    protected array $directives = [];
 
-    public function buildDirectives()
+    protected ?bool $_isDirectivesBuilt;
+
+    public function buildDirectives(): void
     {
         if ($this->_isDirectivesBuilt) {
             return;
@@ -25,15 +26,15 @@ public function buildDirectives()
         if (!empty($this->data['directives'])) {
             $this->addDirectives($this->data['directives']);
         }
+
         $this->_isDirectivesBuilt = true;
     }
 
-    public function addDirectives($directiveList)
+    public function addDirectives($directiveList): static
     {
         foreach ($directiveList as $directiveName => $directiveInfo) {
             if ($directiveInfo instanceof Directive) {
                 $this->directives[$directiveInfo->getName()] = $directiveInfo;
-                continue;
             } else {
                 $this->addDirective($directiveName, $this->buildConfig($directiveName, $directiveInfo));
             }
@@ -42,11 +43,12 @@ public function addDirectives($directiveList)
         return $this;
     }
 
-    public function addDirective($directive, $directiveInfo = null)
+    public function addDirective($directive, $directiveInfo = null): static
     {
         if (!($directive instanceof Directive)) {
             $directive = new Directive($this->buildConfig($directive, $directiveInfo));
         }
+
         $this->directives[$directive->getName()] = $directive;
 
         return $this;
@@ -57,22 +59,20 @@ public function addDirective($directive, $directiveInfo = null)
      *
      * @return InputField
      */
-    public function getDirective($name)
+    public function getDirective($name): ?InputField
     {
         return $this->hasDirective($name) ? $this->directives[$name] : null;
     }
 
     /**
      * @param $name
-     *
-     * @return bool
      */
-    public function hasDirective($name)
+    public function hasDirective($name): bool
     {
         return array_key_exists($name, $this->directives);
     }
 
-    public function hasDirectives()
+    public function hasDirectives(): bool
     {
         return !empty($this->directives);
     }
@@ -80,12 +80,12 @@ public function hasDirectives()
     /**
      * @return InputField[]
      */
-    public function getDirectives()
+    public function getDirectives(): array
     {
         return $this->directives;
     }
 
-    public function removeDirective($name)
+    public function removeDirective($name): static
     {
         if ($this->hasDirective($name)) {
             unset($this->directives[$name]);
@@ -94,4 +94,19 @@ public function removeDirective($name)
         return $this;
     }
 
+    protected function buildConfig($name, $info = null): array
+    {
+        if (!is_array($info)) {
+            return [
+                'type' => $info,
+                'name' => $name
+            ];
+        }
+
+        if (empty($info['name'])) {
+            $info['name'] = $name;
+        }
+
+        return $info;
+    }
 }
diff --git a/src/Config/Traits/FieldsAwareConfigTrait.php b/src/Config/Traits/FieldsAwareConfigTrait.php
index f6d360ff..18f30c60 100644
--- a/src/Config/Traits/FieldsAwareConfigTrait.php
+++ b/src/Config/Traits/FieldsAwareConfigTrait.php
@@ -10,7 +10,6 @@
 
 
 use Youshido\GraphQL\Exception\ConfigurationException;
-use Youshido\GraphQL\Exception\ValidationException;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Field\FieldInterface;
 use Youshido\GraphQL\Field\InputFieldInterface;
@@ -22,9 +21,12 @@
  */
 trait FieldsAwareConfigTrait
 {
-    protected $fields = [];
+    protected array $fields = [];
 
-    public function buildFields()
+    /**
+     * @throws ConfigurationException
+     */
+    public function buildFields(): void
     {
         if (!empty($this->data['fields'])) {
             $this->addFields($this->data['fields']);
@@ -33,10 +35,11 @@ public function buildFields()
 
     /**
      * Add fields from passed interface
-     * @param AbstractInterfaceType $interfaceType
      * @return $this
+     * @throws ConfigurationException
+     * @throws ConfigurationException
      */
-    public function applyInterface(AbstractInterfaceType $interfaceType)
+    public function applyInterface(AbstractInterfaceType $interfaceType): static
     {
         $this->addFields($interfaceType->getFields());
 
@@ -44,19 +47,17 @@ public function applyInterface(AbstractInterfaceType $interfaceType)
     }
 
     /**
-     * @param array $fieldsList
      * @return $this
+     * @throws ConfigurationException
      */
-    public function addFields($fieldsList)
+    public function addFields(array $fieldsList): static
     {
         foreach ($fieldsList as $fieldName => $fieldConfig) {
 
             if ($fieldConfig instanceof FieldInterface) {
                 $this->fields[$fieldConfig->getName()] = $fieldConfig;
-                continue;
-            } elseif($fieldConfig instanceof InputFieldInterface) {
+            } elseif ($fieldConfig instanceof InputFieldInterface) {
                 $this->fields[$fieldConfig->getName()] = $fieldConfig;
-                continue;
             } else {
                 $this->addField($fieldName, $this->buildFieldConfig($fieldName, $fieldConfig));
             }
@@ -66,14 +67,14 @@ public function addFields($fieldsList)
     }
 
     /**
-     * @param FieldInterface|string $field     Field name or Field Object
-     * @param mixed                 $fieldInfo Field Type or Field Config array
+     * @param mixed $field Field name or Field Object
+     * @param null $fieldInfo Field Type or Field Config array
      *
      * @return $this
      *
      * @throws ConfigurationException
      */
-    public function addField($field, $fieldInfo = null)
+    public function addField(mixed $field, $fieldInfo = null): static
     {
         if (!($field instanceof FieldInterface)) {
             $field = new Field($this->buildFieldConfig($field, $fieldInfo));
@@ -82,7 +83,7 @@ public function addField($field, $fieldInfo = null)
         if ($this->hasField($field->getName())) {
             throw new ConfigurationException(sprintf('Type "%s" was defined more than once', $field->getName()));
         }
-        
+
         $this->fields[$field->getName()] = $field;
 
         return $this;
@@ -104,25 +105,21 @@ protected function buildFieldConfig($name, $info = null)
 
     /**
      * @param $name
-     *
-     * @return Field
      */
-    public function getField($name)
+    public function getField($name): mixed
     {
         return $this->hasField($name) ? $this->fields[$name] : null;
     }
 
     /**
      * @param $name
-     *
-     * @return bool
      */
-    public function hasField($name)
+    public function hasField($name): bool
     {
         return array_key_exists($name, $this->fields);
     }
 
-    public function hasFields()
+    public function hasFields(): bool
     {
         return !empty($this->fields);
     }
@@ -130,12 +127,12 @@ public function hasFields()
     /**
      * @return Field[]
      */
-    public function getFields()
+    public function getFields(): array
     {
         return $this->fields;
     }
 
-    public function removeField($name)
+    public function removeField($name): static
     {
         if ($this->hasField($name)) {
             unset($this->fields[$name]);
@@ -143,4 +140,4 @@ public function removeField($name)
 
         return $this;
     }
-}
+}
\ No newline at end of file
diff --git a/src/Config/Traits/ResolvableObjectTrait.php b/src/Config/Traits/ResolvableObjectTrait.php
index 55d8718a..2f1ab5bd 100644
--- a/src/Config/Traits/ResolvableObjectTrait.php
+++ b/src/Config/Traits/ResolvableObjectTrait.php
@@ -7,32 +7,33 @@
 
 namespace Youshido\GraphQL\Config\Traits;
 
+use Exception;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Type\TypeMap;
 use Youshido\GraphQL\Type\TypeService;
 
 trait ResolvableObjectTrait
 {
-
-    public function resolve($value, array $args, ResolveInfo $info)
+    /**
+     * @throws Exception
+     */
+    public function resolve($value, array $args, ResolveInfo $info): mixed
     {
         if ($resolveFunction = $this->getConfig()->getResolveFunction()) {
             return $resolveFunction($value, $args, $info);
+        } elseif (is_array($value) && array_key_exists($this->getName(), $value)) {
+            return $value[$this->getName()];
+        } elseif (is_object($value)) {
+            return TypeService::getPropertyValue($value, $this->getName());
+        } elseif ($this->getType()->getKind() !== TypeMap::KIND_NON_NULL) {
+            return null;
         } else {
-            if (is_array($value) && array_key_exists($this->getName(), $value)) {
-                return $value[$this->getName()];
-            } elseif (is_object($value)) {
-                return TypeService::getPropertyValue($value, $this->getName());
-            } elseif ($this->getType()->getKind() !== TypeMap::KIND_NON_NULL) {
-                return null;
-            } else {
-                throw new \Exception(sprintf('Property "%s" not found in resolve result', $this->getName()));
-            }
+            throw new Exception(sprintf('Property "%s" not found in resolve result', $this->getName()));
         }
     }
 
 
-    public function getResolveFunction()
+    public function getResolveFunction(): ?callable
     {
         return $this->getConfig()->getResolveFunction();
     }
diff --git a/src/Config/TypeConfigInterface.php b/src/Config/TypeConfigInterface.php
index 3312fe31..0ad1e32b 100644
--- a/src/Config/TypeConfigInterface.php
+++ b/src/Config/TypeConfigInterface.php
@@ -12,12 +12,7 @@
 
 interface TypeConfigInterface
 {
-
-    /**
-     * @param Field|string $field
-     * @param array        $fieldInfo
-     */
-    public function addField($field, $fieldInfo = null);
+    public function addField(Field|string $field, ?array $fieldInfo = null);
 
     public function getField($name);
 
diff --git a/src/Directive/Directive.php b/src/Directive/Directive.php
index 5a29569e..2c1b7274 100644
--- a/src/Directive/Directive.php
+++ b/src/Directive/Directive.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Directive;
 
 use Youshido\GraphQL\Config\Directive\DirectiveConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\Traits\ArgumentsAwareObjectTrait;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 
@@ -19,6 +20,9 @@ class Directive implements DirectiveInterface
 
     protected $isFinal = false;
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct(array $config = [])
     {
         if (empty($config['name'])) {
@@ -29,7 +33,7 @@ public function __construct(array $config = [])
         $this->build($this->config);
     }
 
-    public function build(DirectiveConfig $config)
+    public function build(DirectiveConfig $config): void
     {
 
     }
diff --git a/src/Directive/DirectiveInterface.php b/src/Directive/DirectiveInterface.php
index d71b8c09..4821a730 100644
--- a/src/Directive/DirectiveInterface.php
+++ b/src/Directive/DirectiveInterface.php
@@ -24,25 +24,12 @@ public function addArgument($argument, $ArgumentInfo = null);
     /**
      * @return AbstractType[]
      */
-    public function getArguments();
+    public function getArguments(): array;
 
-    /**
-     * @param string $argumentName
-     *
-     * @return AbstractType
-     */
-    public function getArgument($argumentName);
+    public function getArgument(string $argumentName);
 
-    /**
-     * @param string $argumentName
-     *
-     * @return bool
-     */
-    public function hasArgument($argumentName);
+    public function hasArgument(string $argumentName): bool;
 
-    /**
-     * @return boolean
-     */
-    public function hasArguments();
+    public function hasArguments(): bool;
 
 }
diff --git a/src/Directive/DirectiveLocation.php b/src/Directive/DirectiveLocation.php
index 32a0e15d..d3a55875 100644
--- a/src/Directive/DirectiveLocation.php
+++ b/src/Directive/DirectiveLocation.php
@@ -11,12 +11,19 @@
 class DirectiveLocation
 {
 
-    const QUERY = 'QUERY';
-    const MUTATION = 'MUTATION';
-    const FIELD = 'FIELD';
-    const FIELD_DEFINITION = 'FIELD_DEFINITION';
-    const FRAGMENT_DEFINITION = 'FRAGMENT_DEFINITION';
-    const FRAGMENT_SPREAD = 'FRAGMENT_SPREAD';
-    const INLINE_FRAGMENT = 'INLINE_FRAGMENT';
-    const ENUM_VALUE = 'ENUM_VALUE';
+    final const QUERY = 'QUERY';
+
+    final const MUTATION = 'MUTATION';
+
+    final const FIELD = 'FIELD';
+
+    final const FIELD_DEFINITION = 'FIELD_DEFINITION';
+
+    final const FRAGMENT_DEFINITION = 'FRAGMENT_DEFINITION';
+
+    final const FRAGMENT_SPREAD = 'FRAGMENT_SPREAD';
+
+    final const INLINE_FRAGMENT = 'INLINE_FRAGMENT';
+
+    final const ENUM_VALUE = 'ENUM_VALUE';
 }
diff --git a/src/Exception/ConfigurationException.php b/src/Exception/ConfigurationException.php
index 021ae5c2..a9b6d2d2 100644
--- a/src/Exception/ConfigurationException.php
+++ b/src/Exception/ConfigurationException.php
@@ -9,7 +9,9 @@
 namespace Youshido\GraphQL\Exception;
 
 
-class ConfigurationException extends \Exception
+use Exception;
+
+class ConfigurationException extends Exception
 {
 
 }
\ No newline at end of file
diff --git a/src/Exception/Parser/AbstractParserError.php b/src/Exception/Parser/AbstractParserError.php
index 60bdc17b..403dfc6e 100644
--- a/src/Exception/Parser/AbstractParserError.php
+++ b/src/Exception/Parser/AbstractParserError.php
@@ -8,14 +8,14 @@
 namespace Youshido\GraphQL\Exception\Parser;
 
 
+use Exception;
 use Youshido\GraphQL\Exception\Interfaces\LocationableExceptionInterface;
 use Youshido\GraphQL\Parser\Location;
 
-abstract class AbstractParserError extends \Exception implements LocationableExceptionInterface
+abstract class AbstractParserError extends Exception implements LocationableExceptionInterface
 {
 
-    /** @var Location */
-    private $location;
+    private readonly Location $location;
 
     public function __construct($message, Location $location)
     {
diff --git a/src/Exception/ResolveException.php b/src/Exception/ResolveException.php
index 9ff0fc84..45e1acd1 100644
--- a/src/Exception/ResolveException.php
+++ b/src/Exception/ResolveException.php
@@ -8,16 +8,16 @@
 namespace Youshido\GraphQL\Exception;
 
 
+use Exception;
 use Youshido\GraphQL\Exception\Interfaces\LocationableExceptionInterface;
 use Youshido\GraphQL\Parser\Location;
 
-class ResolveException extends \Exception implements LocationableExceptionInterface
+class ResolveException extends Exception implements LocationableExceptionInterface
 {
 
-    /** @var  Location */
-    private $location;
+    private readonly ?Location $location;
 
-    public function __construct($message, Location $location = null)
+    public function __construct($message, ?Location $location = null)
     {
         parent::__construct($message);
 
@@ -26,9 +26,9 @@ public function __construct($message, Location $location = null)
 
 
     /**
-     * @return Location
+     * @return Location|null
      */
-    public function getLocation()
+    public function getLocation(): ?Location
     {
         return $this->location;
     }
diff --git a/src/Exception/ValidationException.php b/src/Exception/ValidationException.php
index 4f1f0e57..5eaac1ab 100644
--- a/src/Exception/ValidationException.php
+++ b/src/Exception/ValidationException.php
@@ -8,7 +8,9 @@
 namespace Youshido\GraphQL\Exception;
 
 
-class ValidationException extends \Exception
+use Exception;
+
+class ValidationException extends Exception
 {
 
 }
\ No newline at end of file
diff --git a/src/Execution/Container/Container.php b/src/Execution/Container/Container.php
index 975f9d1b..ce145614 100644
--- a/src/Execution/Container/Container.php
+++ b/src/Execution/Container/Container.php
@@ -8,18 +8,23 @@
 
 namespace Youshido\GraphQL\Execution\Container;
 
+use Exception;
+use RuntimeException;
+
 class Container implements ContainerInterface
 {
 
-    private $keyset   = [];
-    private $values   = [];
-    private $services = [];
+    private array $keyset = [];
+
+    private array $values = [];
+
+    private array $services = [];
 
 
     /**
      * @param $id
      * @return mixed
-     * @throws \Exception if there was no value set under specified id
+     * @throws Exception if there was no value set under specified id
      */
     public function get($id)
     {
@@ -27,10 +32,11 @@ public function get($id)
         if (isset($this->services['id'])) {
             return $this->services['id']($this);
         }
+
         return $this->values[$id];
     }
 
-    public function set($id, $value)
+    public function set($id, $value): static
     {
         $this->values[$id] = $value;
         $this->keyset[$id] = true;
@@ -40,36 +46,38 @@ public function set($id, $value)
     protected function setAsService($id, $service)
     {
         if (!is_object($service)) {
-            throw new \RuntimeException(sprintf('Service %s has to be an object', $id));
+            throw new RuntimeException(sprintf('Service %s has to be an object', $id));
         }
 
         $this->services[$id] = $service;
         if (isset($this->values[$id])) {
             unset($this->values[$id]);
         }
-        $this->keyset[$id]   = true;
+
+        $this->keyset[$id] = true;
     }
 
-    public function remove($id)
+    public function remove($id): void
     {
         $this->assertIdentifierSet($id);
         if (array_key_exists($id, $this->values)) {
             unset($this->values[$id]);
         }
+
         if (array_key_exists($id, $this->services)) {
             unset($this->services[$id]);
         }
     }
 
-    public function has($id)
+    public function has($id): bool
     {
         return isset($this->keyset[$id]);
     }
 
-    private function assertIdentifierSet($id)
+    private function assertIdentifierSet($id): void
     {
         if (!$this->has($id)) {
-            throw new \RuntimeException(sprintf('Container item "%s" was not set', $id));
+            throw new RuntimeException(sprintf('Container item "%s" was not set', $id));
         }
     }
 }
\ No newline at end of file
diff --git a/src/Execution/Container/ContainerInterface.php b/src/Execution/Container/ContainerInterface.php
index 4f79438a..1d3c9976 100644
--- a/src/Execution/Container/ContainerInterface.php
+++ b/src/Execution/Container/ContainerInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 namespace Youshido\GraphQL\Execution\Container;
 
 interface ContainerInterface
diff --git a/src/Execution/Context/ExecutionContext.php b/src/Execution/Context/ExecutionContext.php
index b5e6381c..24ab1f47 100644
--- a/src/Execution/Context/ExecutionContext.php
+++ b/src/Execution/Context/ExecutionContext.php
@@ -8,7 +8,7 @@
 
 namespace Youshido\GraphQL\Execution\Context;
 
-
+use Exception;
 use Youshido\GraphQL\Execution\Container\ContainerInterface;
 use Youshido\GraphQL\Execution\Request;
 use Youshido\GraphQL\Field\Field;
@@ -21,25 +21,18 @@
 
 class ExecutionContext implements ExecutionContextInterface
 {
-
     use ErrorContainerTrait;
 
-    /** @var AbstractSchema */
-    private $schema;
+    private AbstractSchema $schema;
 
-    /** @var Request */
-    private $request;
+    private ?Request $request = null;
 
-    /** @var ContainerInterface */
-    private $container;
+    private ?ContainerInterface $container = null;
 
-    /** @var array */
-    private $typeFieldLookupTable;
+    private array $typeFieldLookupTable = [];
 
     /**
      * ExecutionContext constructor.
-     *
-     * @param AbstractSchema $schema
      */
     public function __construct(AbstractSchema $schema)
     {
@@ -47,17 +40,12 @@ public function __construct(AbstractSchema $schema)
         $this->validateSchema();
 
         $this->introduceIntrospectionFields();
-
-        $this->typeFieldLookupTable = [];
     }
 
     /**
-     * @param AbstractObjectType $type
-     * @param string             $fieldName
-     * 
-     * @return Field
+     * @return mixed - Field
      */
-    public function getField(AbstractObjectType $type, $fieldName)
+    public function getField(AbstractObjectType $type, string $fieldName): mixed
     {
         $typeName = $type->getName();
 
@@ -72,56 +60,46 @@ public function getField(AbstractObjectType $type, $fieldName)
         return $this->typeFieldLookupTable[$typeName][$fieldName];
     }
 
-    protected function validateSchema()
+    protected function validateSchema(): void
     {
         try {
             (new SchemaValidator())->validate($this->schema);
-        } catch (\Exception $e) {
-            $this->addError($e);
-        };
+        } catch (Exception $exception) {
+            $this->addError($exception);
+        }
     }
 
-    protected function introduceIntrospectionFields()
+    protected function introduceIntrospectionFields(): void
     {
         $schemaField = new SchemaField();
         $this->schema->addQueryField($schemaField);
         $this->schema->addQueryField(new TypeDefinitionField());
     }
 
-    /**
-     * @return AbstractSchema
-     */
-    public function getSchema()
+    public function getSchema(): AbstractSchema
     {
         return $this->schema;
     }
 
     /**
-     * @param AbstractSchema $schema
-     *
      * @return $this
      */
-    public function setSchema(AbstractSchema $schema)
+    public function setSchema(AbstractSchema $schema): static
     {
         $this->schema = $schema;
 
         return $this;
     }
 
-    /**
-     * @return Request
-     */
-    public function getRequest()
+    public function getRequest(): ?Request
     {
         return $this->request;
     }
 
     /**
-     * @param Request $request
-     *
      * @return $this
      */
-    public function setRequest(Request $request)
+    public function setRequest(Request $request): static
     {
         $this->request = $request;
 
@@ -133,23 +111,18 @@ public function get($id)
         return $this->container->get($id);
     }
 
-    /**
-     * @return ContainerInterface
-     */
-    public function getContainer()
+    public function getContainer(): ?ContainerInterface
     {
         return $this->container;
     }
 
     /**
-     * @param ContainerInterface $container
-     *
      * @return $this
      */
-    public function setContainer(ContainerInterface $container)
+    public function setContainer(ContainerInterface $container): static
     {
         $this->container = $container;
 
         return $this;
     }
-}
+}
\ No newline at end of file
diff --git a/src/Execution/Context/ExecutionContextInterface.php b/src/Execution/Context/ExecutionContextInterface.php
index 0845c237..93d9d199 100644
--- a/src/Execution/Context/ExecutionContextInterface.php
+++ b/src/Execution/Context/ExecutionContextInterface.php
@@ -22,8 +22,6 @@ interface ExecutionContextInterface extends ErrorContainerInterface
     public function getSchema();
 
     /**
-     * @param AbstractSchema $schema
-     *
      * @return $this
      */
     public function setSchema(AbstractSchema $schema);
@@ -34,8 +32,6 @@ public function setSchema(AbstractSchema $schema);
     public function getRequest();
 
     /**
-     * @param Request $request
-     *
      * @return $this
      */
     public function setRequest(Request $request);
@@ -46,7 +42,6 @@ public function setRequest(Request $request);
     public function getContainer();
 
     /**
-     * @param ContainerInterface $container
      * @return mixed
      */
     public function setContainer(ContainerInterface $container);
diff --git a/src/Execution/DeferredResolver.php b/src/Execution/DeferredResolver.php
index 9414dac7..99c8e13a 100644
--- a/src/Execution/DeferredResolver.php
+++ b/src/Execution/DeferredResolver.php
@@ -14,7 +14,8 @@
  *
  * @package Youshido\GraphQL\Execution
  */
-class DeferredResolver implements DeferredResolverInterface {
+class DeferredResolver implements DeferredResolverInterface
+{
 
     /** @var callable */
     private $resolver;
@@ -24,7 +25,8 @@ public function __construct($resolver)
         $this->resolver = $resolver;
     }
 
-    public function resolve() {
-      return call_user_func($this->resolver);
+    public function resolve(): mixed
+    {
+        return call_user_func($this->resolver);
     }
 }
\ No newline at end of file
diff --git a/src/Execution/DeferredResolverInterface.php b/src/Execution/DeferredResolverInterface.php
index 63cb80cd..58d74012 100644
--- a/src/Execution/DeferredResolverInterface.php
+++ b/src/Execution/DeferredResolverInterface.php
@@ -14,12 +14,13 @@
  * Fields may return a value implementing this interface to use deferred
  * resolving to optimize query performance.
  */
-interface DeferredResolverInterface {
+interface DeferredResolverInterface
+{
 
-  /**
-   * @return mixed
-   *   The actual result value.
-   */
-  public function resolve();
+    /**
+     * @return mixed
+     *   The actual result value.
+     */
+    public function resolve();
 
 }
diff --git a/src/Execution/DeferredResult.php b/src/Execution/DeferredResult.php
index ffca890b..21ed8271 100644
--- a/src/Execution/DeferredResult.php
+++ b/src/Execution/DeferredResult.php
@@ -8,23 +8,22 @@
 
 namespace Youshido\GraphQL\Execution;
 
-
 /**
  * Wrapper class for deferred resolvers during execution process.
  * Not part of the public API.
  *
  * @internal
  */
-class DeferredResult implements DeferredResolverInterface {
+class DeferredResult implements DeferredResolverInterface
+{
 
-    /** @var \Youshido\GraphQL\Execution\DeferredResolver */
-    private $resolver;
+    /** @var DeferredResolver */
+    private readonly DeferredResolverInterface $resolver;
 
     /** @var callable */
     protected $callback;
 
-    /** @var  mixed */
-    public $result;
+    public mixed $result;
 
     public function __construct(DeferredResolverInterface $resolver, callable $callback)
     {
@@ -32,7 +31,8 @@ public function __construct(DeferredResolverInterface $resolver, callable $callb
         $this->callback = $callback;
     }
 
-    public function resolve() {
+    public function resolve(): void
+    {
         $this->result = call_user_func($this->callback, $this->resolver->resolve());
     }
 }
\ No newline at end of file
diff --git a/src/Execution/Processor.php b/src/Execution/Processor.php
index e4aac98c..c40893d9 100644
--- a/src/Execution/Processor.php
+++ b/src/Execution/Processor.php
@@ -7,10 +7,15 @@
 
 namespace Youshido\GraphQL\Execution;
 
-
+use Exception;
+use InvalidArgumentException;
+use Youshido\GraphQL\Exception\ConfigurationException;
+use Youshido\GraphQL\Exception\Parser\InvalidRequestException;
+use Youshido\GraphQL\Exception\Parser\SyntaxErrorException;
 use Youshido\GraphQL\Exception\ResolveException;
 use Youshido\GraphQL\Execution\Container\Container;
 use Youshido\GraphQL\Execution\Context\ExecutionContext;
+use Youshido\GraphQL\Execution\Context\ExecutionContextInterface;
 use Youshido\GraphQL\Execution\Visitor\MaxComplexityQueryVisitor;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Field\FieldInterface;
@@ -20,6 +25,7 @@
 use Youshido\GraphQL\Parser\Ast\ArgumentValue\Literal as AstLiteral;
 use Youshido\GraphQL\Parser\Ast\ArgumentValue\VariableReference;
 use Youshido\GraphQL\Parser\Ast\Field as AstField;
+use Youshido\GraphQL\Parser\Ast\Fragment;
 use Youshido\GraphQL\Parser\Ast\FragmentReference;
 use Youshido\GraphQL\Parser\Ast\Interfaces\FieldInterface as AstFieldInterface;
 use Youshido\GraphQL\Parser\Ast\Mutation as AstMutation;
@@ -43,25 +49,19 @@
 class Processor
 {
 
-    const TYPE_NAME_QUERY = '__typename';
+    final const TYPE_NAME_QUERY = '__typename';
 
-    /** @var ExecutionContext */
-    protected $executionContext;
+    protected ExecutionContextInterface $executionContext;
 
-    /** @var ResolveValidatorInterface */
-    protected $resolveValidator;
+    protected ResolveValidatorInterface $resolveValidator;
 
-    /** @var  array */
-    protected $data;
+    protected array $data = [];
 
-    /** @var int */
-    protected $maxComplexity;
+    protected ?int $maxComplexity = null;
 
-    /** @var array DeferredResult[] */
-    protected $deferredResultsLeaf = [];
+    protected array $deferredResultsLeaf = [];
 
-    /** @var array DeferredResult[] */
-    protected $deferredResultsComplex = [];
+    protected array $deferredResultsComplex = [];
 
     public function __construct(AbstractSchema $schema)
     {
@@ -73,22 +73,22 @@ public function __construct(AbstractSchema $schema)
         $this->resolveValidator = new ResolveValidator($this->executionContext);
     }
 
-    public function processPayload($payload, $variables = [], $reducers = [])
+    public function processPayload($payload, $variables = [], array $reducers = []): static
     {
         $this->data = [];
 
         try {
             $this->parseAndCreateRequest($payload, $variables);
 
-            if ($this->maxComplexity) {
+            if ($this->maxComplexity !== null && $this->maxComplexity !== 0) {
                 $reducers[] = new MaxComplexityQueryVisitor($this->maxComplexity);
             }
 
-            if ($reducers) {
+            if ($reducers !== []) {
                 $reducer = new Reducer();
                 $reducer->reduceQuery($this->executionContext, $reducers);
             }
-            
+
             // Resolve all queries/operations and merge their data at the end
             $operationResults = [];
 
@@ -97,30 +97,30 @@ public function processPayload($payload, $variables = [], $reducers = [])
                     $operationResults[] = $operationResult;
                 }
             }
-            
+
             $this->data = $this->combineResults($operationResults);
 
             // If the processor found any deferred results, resolve them now.
-            if (!empty($this->data) && (!empty($this->deferredResultsLeaf) || !empty($this->deferredResultsComplex))) {
-              try {
-                  while ($deferredResolver = array_shift($this->deferredResultsComplex)) {
-                      $deferredResolver->resolve();
-                  }
-
-                  // Deferred scalar and enum fields should be resolved last to
-                  // pick up as many as possible for a single batch.
-                  while ($deferredResolver = array_shift($this->deferredResultsLeaf)) {
-                      $deferredResolver->resolve();
-                  }
-              } catch (\Exception $e) {
-                  $this->executionContext->addError($e);
-              } finally {
-                  $this->data = static::unpackDeferredResults($this->data);
-              }
+            if ($this->data !== [] && ($this->deferredResultsLeaf !== [] || $this->deferredResultsComplex !== [])) {
+                try {
+                    while ($deferredResolver = array_shift($this->deferredResultsComplex)) {
+                        $deferredResolver->resolve();
+                    }
+
+                    // Deferred scalar and enum fields should be resolved last to
+                    // pick up as many as possible for a single batch.
+                    while ($deferredResolver = array_shift($this->deferredResultsLeaf)) {
+                        $deferredResolver->resolve();
+                    }
+                } catch (Exception $e) {
+                    $this->executionContext->addError($e);
+                } finally {
+                    $this->data = static::unpackDeferredResults($this->data);
+                }
             }
 
-        } catch (\Exception $e) {
-            $this->executionContext->addError($e);
+        } catch (Exception $exception) {
+            $this->executionContext->addError($exception);
         }
 
         return $this;
@@ -135,7 +135,7 @@ public function processPayload($payload, $variables = [], $reducers = [])
      * @return mixed
      *   The unpacked result.
      */
-    public static function unpackDeferredResults($result)
+    public static function unpackDeferredResults(mixed $result): mixed
     {
         while ($result instanceof DeferredResult) {
             $result = $result->result;
@@ -150,16 +150,20 @@ public static function unpackDeferredResults($result)
         return $result;
     }
 
-    protected function resolveQuery(AstQuery $query)
+    /**
+     * @throws ResolveException
+     * @throws ConfigurationException
+     */
+    protected function resolveQuery(AstQuery $query): array
     {
         $schema = $this->executionContext->getSchema();
-        $type   = $query instanceof AstMutation ? $schema->getMutationType() : $schema->getQueryType();
-        $field  = new Field([
+        $type = $query instanceof AstMutation ? $schema->getMutationType() : $schema->getQueryType();
+        $field = new Field([
             'name' => $query instanceof AstMutation ? 'mutation' : 'query',
             'type' => $type
         ]);
 
-        if (self::TYPE_NAME_QUERY == $query->getName()) {
+        if (self::TYPE_NAME_QUERY === $query->getName()) {
             return [$this->getAlias($query) => $type->getName()];
         }
 
@@ -169,14 +173,17 @@ protected function resolveQuery(AstQuery $query)
         return [$this->getAlias($query) => $value];
     }
 
+    /**
+     * @throws ResolveException
+     */
     protected function resolveField(FieldInterface $field, AstFieldInterface $ast, $parentValue = null, $fromObject = false)
     {
         try {
             /** @var AbstractObjectType $type */
-            $type        = $field->getType();
+            $type = $field->getType();
             $nonNullType = $type->getNullableType();
 
-            if (self::TYPE_NAME_QUERY == $ast->getName()) {
+            if (self::TYPE_NAME_QUERY === $ast->getName()) {
                 return $nonNullType->getName();
             }
 
@@ -218,18 +225,21 @@ protected function resolveField(FieldInterface $field, AstFieldInterface $ast, $
                 default:
                     throw new ResolveException(sprintf('Resolving type with kind "%s" not supported', $kind));
             }
-        } catch (\Exception $e) {
-            $this->executionContext->addError($e);
+        } catch (Exception $exception) {
+            $this->executionContext->addError($exception);
 
             if ($fromObject) {
-                throw $e;
+                throw $exception;
             }
 
             return null;
         }
     }
 
-    private function prepareAstArguments(FieldInterface $field, AstFieldInterface $query, Request $request)
+    /**
+     * @throws ResolveException
+     */
+    private function prepareAstArguments(FieldInterface $field, AstFieldInterface $query, Request $request): void
     {
         foreach ($query->getArguments() as $astArgument) {
             if ($field->hasArgument($astArgument->getName())) {
@@ -240,6 +250,9 @@ private function prepareAstArguments(FieldInterface $field, AstFieldInterface $q
         }
     }
 
+    /**
+     * @throws ResolveException
+     */
     private function prepareArgumentValue($argumentValue, AbstractType $argumentType, Request $request)
     {
         switch ($argumentType->getKind()) {
@@ -251,10 +264,8 @@ private function prepareArgumentValue($argumentValue, AbstractType $argumentType
                     foreach ($list as $item) {
                         $result[] = $this->prepareArgumentValue($item, $argumentType->getItemType()->getNullableType(), $request);
                     }
-                } else {
-                    if ($argumentValue instanceof VariableReference) {
-                        return $this->getVariableReferenceArgumentValue($argumentValue, $argumentType, $request);
-                    }
+                } elseif ($argumentValue instanceof VariableReference) {
+                    return $this->getVariableReferenceArgumentValue($argumentValue, $argumentType, $request);
                 }
 
                 return $result;
@@ -269,6 +280,7 @@ private function prepareArgumentValue($argumentValue, AbstractType $argumentType
                             $result[$field->getName()] = $field->getType()->getNullableType()->parseInputValue($field->getConfig()->get('defaultValue'));
                         }
                     }
+
                     foreach ($argumentValue->getValue() as $key => $item) {
                         if ($argumentType->hasField($key)) {
                             $result[$key] = $this->prepareArgumentValue($item, $argumentType->getField($key)->getType()->getNullableType(), $request);
@@ -276,14 +288,10 @@ private function prepareArgumentValue($argumentValue, AbstractType $argumentType
                             $result[$key] = $item;
                         }
                     }
-                } else {
-                    if ($argumentValue instanceof VariableReference) {
-                        return $this->getVariableReferenceArgumentValue($argumentValue, $argumentType, $request);
-                    } else {
-                        if (is_array($argumentValue)) {
-                            return $argumentValue;
-                        }
-                    }
+                } elseif ($argumentValue instanceof VariableReference) {
+                    return $this->getVariableReferenceArgumentValue($argumentValue, $argumentType, $request);
+                } elseif (is_array($argumentValue)) {
+                    return $argumentValue;
                 }
 
                 return $result;
@@ -293,18 +301,19 @@ private function prepareArgumentValue($argumentValue, AbstractType $argumentType
                 /** @var $argumentValue AstLiteral|VariableReference */
                 if ($argumentValue instanceof VariableReference) {
                     return $this->getVariableReferenceArgumentValue($argumentValue, $argumentType, $request);
+                } elseif ($argumentValue instanceof AstLiteral) {
+                    return $argumentValue->getValue();
                 } else {
-                    if ($argumentValue instanceof AstLiteral) {
-                        return $argumentValue->getValue();
-                    } else {
-                        return $argumentValue;
-                    }
+                    return $argumentValue;
                 }
         }
 
         throw new ResolveException('Argument type not supported');
     }
 
+    /**
+     * @throws ResolveException
+     */
     private function getVariableReferenceArgumentValue(VariableReference $variableReference, AbstractType $argumentType, Request $request)
     {
         $variable = $variableReference->getVariable();
@@ -316,10 +325,8 @@ private function getVariableReferenceArgumentValue(VariableReference $variableRe
             ) {
                 throw new ResolveException(sprintf('Invalid variable "%s" type, allowed type is "%s"', $variable->getName(), $argumentType->getNamedType()->getNullableType()->getName()), $variable->getLocation());
             }
-        } else {
-            if ($variable->getTypeName() !== $argumentType->getName()) {
-                throw new ResolveException(sprintf('Invalid variable "%s" type, allowed type is "%s"', $variable->getName(), $argumentType->getName()), $variable->getLocation());
-            }
+        } elseif ($variable->getTypeName() !== $argumentType->getName()) {
+            throw new ResolveException(sprintf('Invalid variable "%s" type, allowed type is "%s"', $variable->getName(), $argumentType->getName()), $variable->getLocation());
         }
 
         $requestValue = $request->getVariable($variable->getName());
@@ -332,20 +339,17 @@ private function getVariableReferenceArgumentValue(VariableReference $variableRe
 
 
     /**
-     * @param FieldInterface     $field
-     * @param AbstractObjectType $type
-     * @param AstFieldInterface  $ast
-     * @param                    $resolvedValue
-     * @return array
+     * @param $resolvedValue
+     * @throws ResolveException
      */
-    private function collectResult(FieldInterface $field, AbstractObjectType $type, $ast, $resolvedValue)
+    private function collectResult(FieldInterface $field, AbstractObjectType $type, Fragment|AstFieldInterface|TypedFragmentReference $ast, $resolvedValue): array
     {
         $results = [];
 
         foreach ($ast->getFields() as $astField) {
             switch (true) {
                 case $astField instanceof TypedFragmentReference:
-                    $astName  = $astField->getTypeName();
+                    $astName = $astField->getTypeName();
                     $typeName = $type->getName();
 
                     if ($typeName !== $astName) {
@@ -365,9 +369,9 @@ private function collectResult(FieldInterface $field, AbstractObjectType $type,
                     break;
 
                 case $astField instanceof FragmentReference:
-                    $astFragment      = $this->executionContext->getRequest()->getFragment($astField->getName());
+                    $astFragment = $this->executionContext->getRequest()->getFragment($astField->getName());
                     $astFragmentModel = $astFragment->getModel();
-                    $typeName         = $type->getName();
+                    $typeName = $type->getName();
 
                     if ($typeName !== $astFragmentModel) {
                         foreach ($type->getInterfaces() as $interface) {
@@ -396,7 +400,8 @@ private function collectResult(FieldInterface $field, AbstractObjectType $type,
     /**
      * Apply post-process callbacks to all deferred resolvers.
      */
-    protected function deferredResolve($resolvedValue, FieldInterface $field, callable $callback) {
+    protected function deferredResolve($resolvedValue, FieldInterface $field, callable $callback): mixed
+    {
         if ($resolvedValue instanceof DeferredResolverInterface) {
             $deferredResult = new DeferredResult($resolvedValue, function ($resolvedValue) use ($field, $callback) {
                 // Allow nested deferred resolvers.
@@ -414,14 +419,19 @@ protected function deferredResolve($resolvedValue, FieldInterface $field, callab
 
             return $deferredResult;
         }
+
         // For simple values, invoke the callback immediately.
         return $callback($resolvedValue);
     }
 
-    protected function resolveScalar(FieldInterface $field, AstFieldInterface $ast, $parentValue)
+    /**
+     * @param $parentValue
+     * @throws ResolveException
+     */
+    protected function resolveScalar(FieldInterface $field, AstFieldInterface $ast, $parentValue): mixed
     {
         $resolvedValue = $this->doResolve($field, $ast, $parentValue);
-        return $this->deferredResolve($resolvedValue, $field, function($resolvedValue) use ($field) {
+        return $this->deferredResolve($resolvedValue, $field, function ($resolvedValue) use ($field) {
             $this->resolveValidator->assertValidResolvedValueForField($field, $resolvedValue);
 
             /** @var AbstractScalarType $type */
@@ -431,12 +441,17 @@ protected function resolveScalar(FieldInterface $field, AstFieldInterface $ast,
         });
     }
 
-    protected function resolveList(FieldInterface $field, AstFieldInterface $ast, $parentValue)
+    /**
+     * @param $parentValue
+     * @throws ResolveException
+     * @throws ConfigurationException
+     */
+    protected function resolveList(FieldInterface $field, AstFieldInterface $ast, $parentValue): mixed
     {
         /** @var AstQuery $ast */
         $resolvedValue = $this->doResolve($field, $ast, $parentValue);
 
-        return $this->deferredResolve($resolvedValue, $field, function ($resolvedValue) use ($field, $ast) {
+        return $this->deferredResolve($resolvedValue, $field, function ($resolvedValue) use ($field, $ast): ?array {
             $this->resolveValidator->assertValidResolvedValueForField($field, $resolvedValue);
 
             if (null === $resolvedValue) {
@@ -444,7 +459,7 @@ protected function resolveList(FieldInterface $field, AstFieldInterface $ast, $p
             }
 
             /** @var AbstractListType $type */
-            $type     = $field->getType()->getNullableType();
+            $type = $field->getType()->getNullableType();
             $itemType = $type->getNamedType();
 
             $fakeAst = clone $ast;
@@ -453,41 +468,25 @@ protected function resolveList(FieldInterface $field, AstFieldInterface $ast, $p
             }
 
             $fakeField = new Field([
-              'name' => $field->getName(),
-              'type' => $itemType,
-              'args' => $field->getArguments(),
+                'name' => $field->getName(),
+                'type' => $itemType,
+                'args' => $field->getArguments(),
             ]);
 
             $result = [];
             foreach ($resolvedValue as $resolvedValueItem) {
                 try {
-                    $fakeField->getConfig()->set('resolve', function () use ($resolvedValueItem) {
+                    $fakeField->getConfig()->set('resolve', static function () use ($resolvedValueItem) {
                         return $resolvedValueItem;
                     });
 
-                    switch ($itemType->getNullableType()->getKind()) {
-                        case TypeMap::KIND_ENUM:
-                        case TypeMap::KIND_SCALAR:
-                            $value = $this->resolveScalar($fakeField, $fakeAst, $resolvedValueItem);
-
-                            break;
-
-
-                        case TypeMap::KIND_OBJECT:
-                            $value = $this->resolveObject($fakeField, $fakeAst, $resolvedValueItem);
-
-                            break;
-
-                        case TypeMap::KIND_UNION:
-                        case TypeMap::KIND_INTERFACE:
-                            $value = $this->resolveComposite($fakeField, $fakeAst, $resolvedValueItem);
-
-                            break;
-
-                        default:
-                            $value = null;
-                    }
-                } catch (\Exception $e) {
+                    $value = match ($itemType->getNullableType()->getKind()) {
+                        TypeMap::KIND_ENUM, TypeMap::KIND_SCALAR => $this->resolveScalar($fakeField, $fakeAst, $resolvedValueItem),
+                        TypeMap::KIND_OBJECT => $this->resolveObject($fakeField, $fakeAst, $resolvedValueItem),
+                        TypeMap::KIND_UNION, TypeMap::KIND_INTERFACE => $this->resolveComposite($fakeField, $fakeAst, $resolvedValueItem),
+                        default => null,
+                    };
+                } catch (Exception $e) {
                     $this->executionContext->addError($e);
 
                     $value = null;
@@ -500,31 +499,41 @@ protected function resolveList(FieldInterface $field, AstFieldInterface $ast, $p
         });
     }
 
-    protected function resolveObject(FieldInterface $field, AstFieldInterface $ast, $parentValue, $fromUnion = false)
+    /**
+     * @param $parentValue
+     * @throws ResolveException
+     */
+    protected function resolveObject(FieldInterface $field, AstFieldInterface $ast, $parentValue, bool $fromUnion = false): mixed
     {
         $resolvedValue = $parentValue;
         if (!$fromUnion) {
             $resolvedValue = $this->doResolve($field, $ast, $parentValue);
         }
 
-        return $this->deferredResolve($resolvedValue, $field, function ($resolvedValue) use ($field, $ast) {
+        return $this->deferredResolve($resolvedValue, $field, function ($resolvedValue) use ($field, $ast): ?array {
             $this->resolveValidator->assertValidResolvedValueForField($field, $resolvedValue);
 
             if (null === $resolvedValue) {
                 return null;
             }
+
             /** @var AbstractObjectType $type */
             $type = $field->getType()->getNullableType();
 
             try {
                 return $this->collectResult($field, $type, $ast, $resolvedValue);
-            } catch (\Exception $e) {
+            } catch (Exception) {
                 return null;
             }
         });
     }
 
-    protected function resolveComposite(FieldInterface $field, AstFieldInterface $ast, $parentValue)
+    /**
+     * @param $parentValue
+     * @throws ResolveException
+     * @throws ConfigurationException
+     */
+    protected function resolveComposite(FieldInterface $field, AstFieldInterface $ast, $parentValue): mixed
     {
         /** @var AstQuery $ast */
         $resolvedValue = $this->doResolve($field, $ast, $parentValue);
@@ -536,13 +545,8 @@ protected function resolveComposite(FieldInterface $field, AstFieldInterface $as
             }
 
             /** @var AbstractUnionType $type */
-            $type         = $field->getType()->getNullableType();
-            $resolveInfo = new ResolveInfo(
-                $field,
-                $ast instanceof AstQuery ? $ast->getFields() : [],
-                $this->executionContext
-            );
-            $resolvedType = $type->resolveType($resolvedValue, $resolveInfo);
+            $type = $field->getType()->getNullableType();
+            $resolvedType = $type->resolveType($resolvedValue);
 
             if (!$resolvedType) {
                 throw new ResolveException('Resolving function must return type');
@@ -555,22 +559,26 @@ protected function resolveComposite(FieldInterface $field, AstFieldInterface $as
             }
 
             $fakeField = new Field([
-              'name' => $field->getName(),
-              'type' => $resolvedType,
-              'args' => $field->getArguments(),
+                'name' => $field->getName(),
+                'type' => $resolvedType,
+                'args' => $field->getArguments(),
             ]);
 
             return $this->resolveObject($fakeField, $ast, $resolvedValue, true);
         });
     }
 
-    protected function parseAndCreateRequest($payload, $variables = [])
+    /**
+     * @throws SyntaxErrorException
+     * @throws InvalidRequestException
+     */
+    protected function parseAndCreateRequest($payload, $variables = []): void
     {
         if (empty($payload)) {
-            throw new \InvalidArgumentException('Must provide an operation.');
+            throw new InvalidArgumentException('Must provide an operation.');
         }
 
-        $parser  = new Parser();
+        $parser = new Parser();
         $request = new Request($parser->parse($payload), $variables);
 
         (new RequestValidator())->validate($request);
@@ -578,7 +586,7 @@ protected function parseAndCreateRequest($payload, $variables = [])
         $this->executionContext->setRequest($request);
     }
 
-    protected function doResolve(FieldInterface $field, AstFieldInterface $ast, $parentValue = null)
+    protected function doResolve(FieldInterface $field, AstFieldInterface $ast, $parentValue = null): mixed
     {
         /** @var AstQuery|AstField $ast */
         $arguments = $this->parseArgumentsValues($field, $ast);
@@ -587,9 +595,9 @@ protected function doResolve(FieldInterface $field, AstFieldInterface $ast, $par
         return $field->resolve($parentValue, $arguments, $this->createResolveInfo($field, $astFields));
     }
 
-    protected function parseArgumentsValues(FieldInterface $field, AstFieldInterface $ast)
+    protected function parseArgumentsValues(FieldInterface $field, AstFieldInterface $ast): array
     {
-        $values   = [];
+        $values = [];
         $defaults = [];
 
         foreach ($field->getArguments() as $argument) {
@@ -600,7 +608,7 @@ protected function parseArgumentsValues(FieldInterface $field, AstFieldInterface
         }
 
         foreach ($ast->getArguments() as $astArgument) {
-            $argument     = $field->getArgument($astArgument->getName());
+            $argument = $field->getArgument($astArgument->getName());
             $argumentType = $argument->getType()->getNullableType();
 
             $values[$argument->getName()] = $argumentType->parseValue($astArgument->getValue());
@@ -613,27 +621,23 @@ protected function parseArgumentsValues(FieldInterface $field, AstFieldInterface
         return array_merge($values, $defaults);
     }
 
-    private function getAlias(AstFieldInterface $ast)
+    private function getAlias(AstFieldInterface $ast): string
     {
         return $ast->getAlias() ?: $ast->getName();
     }
 
-    protected function createResolveInfo(FieldInterface $field, array $astFields)
+    protected function createResolveInfo(FieldInterface $field, array $astFields): ResolveInfo
     {
         return new ResolveInfo($field, $astFields, $this->executionContext);
     }
 
     /**
      * Combines the specified results using array_replace_recursive, including graceful handling for empty arrays
-     *
-     * @param array $results
-     *
-     * @return array
      */
-    protected function combineResults(array $results)
+    protected function combineResults(array $results): array
     {
-        if (count($results) > 0) {
-            return call_user_func_array('array_replace_recursive', $results);
+        if ($results !== []) {
+            return array_replace_recursive(...$results);
         }
 
         return [];
@@ -641,19 +645,17 @@ protected function combineResults(array $results)
 
     /**
      * You can access ExecutionContext to check errors and inject dependencies
-     *
-     * @return ExecutionContext
      */
-    public function getExecutionContext()
+    public function getExecutionContext(): ExecutionContext
     {
         return $this->executionContext;
     }
 
-    public function getResponseData()
+    public function getResponseData(): array
     {
         $result = [];
 
-        if (!empty($this->data)) {
+        if ($this->data !== []) {
             $result['data'] = $this->data;
         }
 
@@ -664,20 +666,13 @@ public function getResponseData()
         return $result;
     }
 
-    /**
-     * @return int
-     */
-    public function getMaxComplexity()
+    public function getMaxComplexity(): ?int
     {
         return $this->maxComplexity;
     }
 
-    /**
-     * @param int $maxComplexity
-     */
-    public function setMaxComplexity($maxComplexity)
+    public function setMaxComplexity(?int $maxComplexity): void
     {
         $this->maxComplexity = $maxComplexity;
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Execution/Reducer.php b/src/Execution/Reducer.php
index a74c122e..7763544f 100644
--- a/src/Execution/Reducer.php
+++ b/src/Execution/Reducer.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Execution;
 
 
+use Generator;
 use Youshido\GraphQL\Execution\Context\ExecutionContextInterface;
 use Youshido\GraphQL\Execution\Visitor\AbstractQueryVisitor;
 use Youshido\GraphQL\Field\Field;
@@ -24,20 +25,18 @@
 class Reducer
 {
 
-    /** @var  ExecutionContextInterface */
-    private $executionContext;
+    private ?ExecutionContextInterface $executionContext = null;
 
     /**
      * Apply all of $reducers to this query.  Example reducer operations: checking for maximum query complexity,
      * performing look-ahead query planning, etc.
      *
-     * @param ExecutionContextInterface $executionContext
-     * @param AbstractQueryVisitor[]    $reducers
+     * @param AbstractQueryVisitor[] $reducers
      */
-    public function reduceQuery(ExecutionContextInterface $executionContext, array $reducers)
+    public function reduceQuery(ExecutionContextInterface $executionContext, array $reducers): void
     {
         $this->executionContext = $executionContext;
-        $schema                 = $executionContext->getSchema();
+        $schema = $executionContext->getSchema();
 
         foreach ($reducers as $reducer) {
             foreach ($executionContext->getRequest()->getAllOperations() as $operation) {
@@ -50,8 +49,7 @@ public function reduceQuery(ExecutionContextInterface $executionContext, array $
      * Entry point for the `walkQuery` routine.  Execution bounces between here, where the reducer's ->visit() method
      * is invoked, and `walkQuery` where we send in the scores from the `visit` call.
      *
-     * @param Query                $query
-     * @param AbstractType         $currentLevelSchema
+     * @param AbstractType $currentLevelSchema
      * @param AbstractQueryVisitor $reducer
      */
     protected function doVisit(Query $query, $currentLevelSchema, $reducer)
@@ -72,7 +70,7 @@ protected function doVisit(Query $query, $currentLevelSchema, $reducer)
 
                     /**
                      * @var Query|FieldAst $queryField
-                     * @var Field          $astField
+                     * @var Field $astField
                      */
                     $cost = $reducer->visit($queryField->getKeyValueArguments(), $astField->getConfig(), $childCost);
                     $queryCost += $cost;
@@ -92,10 +90,9 @@ protected function doVisit(Query $query, $currentLevelSchema, $reducer)
      * Fragments (anonymous and named), and Fields.  The core of the function is simple: recurse until we hit the base
      * case of a Field and yield that back up to the visitor up in `doVisit`.
      *
-     * @param Query|Field|\Youshido\GraphQL\Parser\Ast\Interfaces\FragmentInterface $queryNode
-     * @param FieldInterface                                                        $currentLevelAST
+     * @param Query|Field|FragmentInterface $queryNode
      *
-     * @return \Generator
+     * @return Generator
      */
     protected function walkQuery($queryNode, FieldInterface $currentLevelAST)
     {
@@ -106,11 +103,12 @@ protected function walkQuery($queryNode, FieldInterface $currentLevelAST)
                     if ($queryField instanceof FragmentReference) {
                         $queryField = $this->executionContext->getRequest()->getFragment($queryField->getName());
                     }
+
                     // the next 7 lines are essentially equivalent to `yield from $this->walkQuery(...)` in PHP7.
                     // for backwards compatibility this is equivalent.
                     // This pattern is repeated multiple times in this function, and unfortunately cannot be extracted or
                     // made less verbose.
-                    $gen  = $this->walkQuery($queryField, $currentLevelAST);
+                    $gen = $this->walkQuery($queryField, $currentLevelAST);
                     $next = $gen->current();
                     while ($next) {
                         $received = (yield $next);
@@ -122,7 +120,7 @@ protected function walkQuery($queryNode, FieldInterface $currentLevelAST)
                     if ($fieldType instanceof AbstractUnionType) {
                         foreach ($fieldType->getTypes() as $unionFieldType) {
                             if ($fieldAst = $unionFieldType->getField($queryField->getName())) {
-                                $gen  = $this->walkQuery($queryField, $fieldAst);
+                                $gen = $this->walkQuery($queryField, $fieldAst);
                                 $next = $gen->current();
                                 while ($next) {
                                     $received = (yield $next);
@@ -132,7 +130,7 @@ protected function walkQuery($queryNode, FieldInterface $currentLevelAST)
                             }
                         }
                     } elseif ($fieldType instanceof AbstractObjectType && $fieldAst = $fieldType->getField($queryField->getName())) {
-                        $gen  = $this->walkQuery($queryField, $fieldAst);
+                        $gen = $this->walkQuery($queryField, $fieldAst);
                         $next = $gen->current();
                         while ($next) {
                             $received = (yield $next);
@@ -143,6 +141,7 @@ protected function walkQuery($queryNode, FieldInterface $currentLevelAST)
                 }
             }
         }
+
         // sanity check.  don't yield fragments; they don't contribute to cost
         if ($queryNode instanceof Query || $queryNode instanceof FieldAst) {
             // BASE CASE.  If we're here we're done recursing -
diff --git a/src/Execution/Request.php b/src/Execution/Request.php
index 5b3da1a0..9479087b 100644
--- a/src/Execution/Request.php
+++ b/src/Execution/Request.php
@@ -19,27 +19,28 @@ class Request
 {
 
     /** @var  Query[] */
-    private $queries = [];
+    private array $queries = [];
 
     /** @var Fragment[] */
-    private $fragments = [];
+    private array $fragments = [];
 
     /** @var Mutation[] */
-    private $mutations = [];
+    private array $mutations = [];
 
     /** @var array */
     private $variables = [];
 
     /** @var VariableReference[] */
-    private $variableReferences = [];
+    private array $variableReferences = [];
 
-    /** @var  array */
-    private $queryVariables = [];
+    private array $queryVariables = [];
 
-    /** @var array */
-    private $fragmentReferences = [];
+    private array $fragmentReferences = [];
 
-    public function __construct($data = [], $variables = [])
+    /**
+     * @throws InvalidRequestException
+     */
+    public function __construct(array $data = [], array $variables = [])
     {
         if (array_key_exists('queries', $data)) {
             $this->addQueries($data['queries']);
@@ -70,6 +71,7 @@ public function __construct($data = [], $variables = [])
                         $variables[$variable->getName()] = $variable->getDefaultValue()->getValue();
                         continue;
                     }
+
                     throw new InvalidRequestException(sprintf("Variable %s hasn't been submitted", $ref->getName()), $ref->getLocation());
                 }
             }
@@ -80,42 +82,42 @@ public function __construct($data = [], $variables = [])
         $this->setVariables($variables);
     }
 
-    public function addQueries($queries)
+    public function addQueries($queries): void
     {
         foreach ($queries as $query) {
             $this->queries[] = $query;
         }
     }
 
-    public function addMutations($mutations)
+    public function addMutations($mutations): void
     {
         foreach ($mutations as $mutation) {
             $this->mutations[] = $mutation;
         }
     }
 
-    public function addQueryVariables($queryVariables)
+    public function addQueryVariables($queryVariables): void
     {
         foreach ($queryVariables as $queryVariable) {
             $this->queryVariables[] = $queryVariable;
         }
     }
 
-    public function addVariableReferences($variableReferences)
+    public function addVariableReferences($variableReferences): void
     {
         foreach ($variableReferences as $variableReference) {
             $this->variableReferences[] = $variableReference;
         }
     }
 
-    public function addFragmentReferences($fragmentReferences)
+    public function addFragmentReferences($fragmentReferences): void
     {
         foreach ($fragmentReferences as $fragmentReference) {
             $this->fragmentReferences[] = $fragmentReference;
         }
     }
 
-    public function addFragments($fragments)
+    public function addFragments($fragments): void
     {
         foreach ($fragments as $fragment) {
             $this->addFragment($fragment);
@@ -125,7 +127,7 @@ public function addFragments($fragments)
     /**
      * @return Query[]
      */
-    public function getAllOperations()
+    public function getAllOperations(): array
     {
         return array_merge($this->mutations, $this->queries);
     }
@@ -133,7 +135,7 @@ public function getAllOperations()
     /**
      * @return Query[]
      */
-    public function getQueries()
+    public function getQueries(): array
     {
         return $this->queries;
     }
@@ -141,22 +143,20 @@ public function getQueries()
     /**
      * @return Fragment[]
      */
-    public function getFragments()
+    public function getFragments(): array
     {
         return $this->fragments;
     }
 
-    public function addFragment(Fragment $fragment)
+    public function addFragment(Fragment $fragment): void
     {
         $this->fragments[] = $fragment;
     }
 
     /**
      * @param $name
-     *
-     * @return null|Fragment
      */
-    public function getFragment($name)
+    public function getFragment($name): ?Fragment
     {
         foreach ($this->fragments as $fragment) {
             if ($fragment->getName() == $name) {
@@ -170,31 +170,22 @@ public function getFragment($name)
     /**
      * @return Mutation[]
      */
-    public function getMutations()
+    public function getMutations(): array
     {
         return $this->mutations;
     }
 
-    /**
-     * @return bool
-     */
-    public function hasQueries()
+    public function hasQueries(): bool
     {
         return (bool)count($this->queries);
     }
 
-    /**
-     * @return bool
-     */
-    public function hasMutations()
+    public function hasMutations(): bool
     {
         return (bool)count($this->mutations);
     }
 
-    /**
-     * @return bool
-     */
-    public function hasFragments()
+    public function hasFragments(): bool
     {
         return (bool)count($this->fragments);
     }
@@ -212,7 +203,7 @@ public function getVariables()
      *
      * @return $this
      */
-    public function setVariables($variables)
+    public function setVariables($variables): static
     {
         if (!is_array($variables)) {
             $variables = json_decode($variables, true);
@@ -221,11 +212,16 @@ public function setVariables($variables)
         $this->variables = $variables;
         foreach ($this->variableReferences as $reference) {
             /** invalid request with no variable */
-            if (!$reference->getVariable()) continue;
+            if (!$reference->getVariable()) {
+                continue;
+            }
+
             $variableName = $reference->getVariable()->getName();
 
             /** no variable was set at the time */
-            if (!array_key_exists($variableName, $variables)) continue;
+            if (!array_key_exists($variableName, $variables)) {
+                continue;
+            }
 
             $reference->getVariable()->setValue($variables[$variableName]);
             $reference->setValue($variables[$variableName]);
@@ -239,7 +235,7 @@ public function getVariable($name)
         return $this->hasVariable($name) ? $this->variables[$name] : null;
     }
 
-    public function hasVariable($name)
+    public function hasVariable($name): bool
     {
         return array_key_exists($name, $this->variables);
     }
@@ -247,15 +243,12 @@ public function hasVariable($name)
     /**
      * @return array|Variable[]
      */
-    public function getQueryVariables()
+    public function getQueryVariables(): array
     {
         return $this->queryVariables;
     }
 
-    /**
-     * @param array $queryVariables
-     */
-    public function setQueryVariables($queryVariables)
+    public function setQueryVariables(array $queryVariables): void
     {
         $this->queryVariables = $queryVariables;
     }
@@ -263,15 +256,12 @@ public function setQueryVariables($queryVariables)
     /**
      * @return array|FragmentReference[]
      */
-    public function getFragmentReferences()
+    public function getFragmentReferences(): array
     {
         return $this->fragmentReferences;
     }
 
-    /**
-     * @param array $fragmentReferences
-     */
-    public function setFragmentReferences($fragmentReferences)
+    public function setFragmentReferences(array $fragmentReferences): void
     {
         $this->fragmentReferences = $fragmentReferences;
     }
@@ -279,7 +269,7 @@ public function setFragmentReferences($fragmentReferences)
     /**
      * @return array|VariableReference[]
      */
-    public function getVariableReferences()
+    public function getVariableReferences(): array
     {
         return $this->variableReferences;
     }
diff --git a/src/Execution/ResolveInfo.php b/src/Execution/ResolveInfo.php
index aa9cc21b..4402be05 100644
--- a/src/Execution/ResolveInfo.php
+++ b/src/Execution/ResolveInfo.php
@@ -16,14 +16,12 @@
 
 class ResolveInfo
 {
-    /** @var  FieldInterface */
-    protected $field;
+    protected FieldInterface $field;
 
     /** @var Field[] */
-    protected $fieldASTList;
+    protected array $fieldASTList;
 
-    /** @var ExecutionContextInterface */
-    protected $executionContext;
+    protected ExecutionContextInterface $executionContext;
 
     /**
      * This property is to be used for DI in various scenario
@@ -36,23 +34,17 @@ class ResolveInfo
 
     public function __construct(FieldInterface $field, array $fieldASTList, ExecutionContextInterface $executionContext)
     {
-        $this->field            = $field;
-        $this->fieldASTList     = $fieldASTList;
+        $this->field = $field;
+        $this->fieldASTList = $fieldASTList;
         $this->executionContext = $executionContext;
     }
 
-    /**
-     * @return ExecutionContextInterface
-     */
-    public function getExecutionContext()
+    public function getExecutionContext(): ExecutionContextInterface
     {
         return $this->executionContext;
     }
 
-    /**
-     * @return FieldInterface
-     */
-    public function getField()
+    public function getField(): FieldInterface
     {
         return $this->field;
     }
@@ -78,7 +70,7 @@ public function getFieldAST($fieldName)
     /**
      * @return Field[]
      */
-    public function getFieldASTList()
+    public function getFieldASTList(): array
     {
         return $this->fieldASTList;
     }
@@ -86,7 +78,7 @@ public function getFieldASTList()
     /**
      * @return AbstractType
      */
-    public function getReturnType()
+    public function getReturnType(): mixed
     {
         return $this->field->getType();
     }
diff --git a/src/Execution/Visitor/AbstractQueryVisitor.php b/src/Execution/Visitor/AbstractQueryVisitor.php
index 5b19f137..c40d2254 100644
--- a/src/Execution/Visitor/AbstractQueryVisitor.php
+++ b/src/Execution/Visitor/AbstractQueryVisitor.php
@@ -59,9 +59,7 @@ public function getMemo()
     /**
      * Visit a query node.  See class docstring.
      *
-     * @param array       $args
-     * @param FieldConfig $fieldConfig
-     * @param int         $childScore
+     * @param int $childScore
      *
      * @return int|null
      */
diff --git a/src/Execution/Visitor/MaxComplexityQueryVisitor.php b/src/Execution/Visitor/MaxComplexityQueryVisitor.php
index 242193fe..045e1060 100644
--- a/src/Execution/Visitor/MaxComplexityQueryVisitor.php
+++ b/src/Execution/Visitor/MaxComplexityQueryVisitor.php
@@ -11,28 +11,27 @@
 
 namespace Youshido\GraphQL\Execution\Visitor;
 
-
+use Exception;
 use Youshido\GraphQL\Config\Field\FieldConfig;
 
 class MaxComplexityQueryVisitor extends AbstractQueryVisitor
 {
-
     /**
-     * @var int max score allowed before throwing an exception (causing processing to stop)
+     * @var ?int max score allowed before throwing an exception (causing processing to stop)
      */
-    public $maxScore;
+    public ?int $maxScore;
 
     /**
      * @var int default score for nodes without explicit cost functions
      */
-    protected $defaultScore = 1;
+    protected int $defaultScore = 1;
 
     /**
      * MaxComplexityQueryVisitor constructor.
      *
-     * @param int $max max allowed complexity score
+     * @param int|null $max max allowed complexity score
      */
-    public function __construct($max)
+    public function __construct(?int $max)
     {
         parent::__construct();
 
@@ -41,10 +40,11 @@ public function __construct($max)
 
     /**
      * {@inheritdoc}
+     * @throws Exception
      */
     public function visit(array $args, FieldConfig $fieldConfig, $childScore = 0)
     {
-        $cost = $fieldConfig->get('cost', null);
+        $cost = $fieldConfig->get('cost');
         if (is_callable($cost)) {
             $cost = $cost($args, $fieldConfig, $childScore);
         }
@@ -52,8 +52,8 @@ public function visit(array $args, FieldConfig $fieldConfig, $childScore = 0)
         $cost = is_null($cost) ? $this->defaultScore : $cost;
         $this->memo += $cost;
 
-        if ($this->memo > $this->maxScore) {
-            throw new \Exception('query exceeded max allowed complexity of ' . $this->maxScore);
+        if ($this->maxScore !== null && $this->maxScore !== 0 && $this->memo > $this->maxScore) {
+            throw new Exception('query exceeded max allowed complexity of ' . $this->maxScore);
         }
 
         return $cost;
diff --git a/src/Field/AbstractField.php b/src/Field/AbstractField.php
index 44a68d1f..62830fc8 100644
--- a/src/Field/AbstractField.php
+++ b/src/Field/AbstractField.php
@@ -9,8 +9,7 @@
 
 use Youshido\GraphQL\Config\Field\FieldConfig;
 use Youshido\GraphQL\Config\Traits\ResolvableObjectTrait;
-use Youshido\GraphQL\Type\AbstractType;
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 use Youshido\GraphQL\Type\Traits\FieldsArgumentsAwareObjectTrait;
 use Youshido\GraphQL\Type\TypeFactory;
@@ -18,45 +17,48 @@
 
 abstract class AbstractField implements FieldInterface
 {
-
     use FieldsArgumentsAwareObjectTrait;
     use ResolvableObjectTrait;
     use AutoNameTrait {
         getName as getAutoName;
     }
-    protected $isFinal = false;
 
-    private $nameCache            = null;
+    protected bool $isFinal = false;
+
+    private mixed $nameCache = null;
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct(array $config = [])
     {
         if (empty($config['type'])) {
             $config['type'] = $this->getType();
             $config['name'] = $this->getName();
             if (empty($config['name'])) {
-                $config['name'] =$this->getAutoName();
+                $config['name'] = $this->getAutoName();
             }
         }
 
         if (TypeService::isScalarType($config['type'])) {
             $config['type'] = TypeFactory::getScalarType($config['type']);
         }
-        $this->nameCache = isset($config['name']) ? $config['name'] : $this->getAutoName();
+
+        if (!$this->nameCache) {
+            $this->nameCache = $config['name'] ?? $this->getAutoName();
+        }
 
         $this->config = new FieldConfig($config, $this, $this->isFinal);
         $this->build($this->config);
     }
 
-    /**
-     * @return AbstractObjectType|AbstractType
-     */
-    abstract public function getType();
+    abstract public function getType(): mixed;
 
-    public function build(FieldConfig $config)
+    public function build(FieldConfig $config): void
     {
     }
 
-    public function setType($type)
+    public function setType($type): void
     {
         $this->getConfig()->set('type', $type);
     }
diff --git a/src/Field/AbstractInputField.php b/src/Field/AbstractInputField.php
index 110acec8..8529d0de 100644
--- a/src/Field/AbstractInputField.php
+++ b/src/Field/AbstractInputField.php
@@ -7,9 +7,9 @@
 
 namespace Youshido\GraphQL\Field;
 
-
 use Youshido\GraphQL\Config\Field\InputFieldConfig;
-use Youshido\GraphQL\Type\InputTypeInterface;
+use Youshido\GraphQL\Exception\ConfigurationException;
+use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 use Youshido\GraphQL\Type\Traits\FieldsArgumentsAwareObjectTrait;
 use Youshido\GraphQL\Type\TypeFactory;
@@ -18,10 +18,14 @@
 abstract class AbstractInputField implements InputFieldInterface
 {
 
-    use FieldsArgumentsAwareObjectTrait, AutoNameTrait;
+    use FieldsArgumentsAwareObjectTrait;
+    use AutoNameTrait;
 
-    protected $isFinal = false;
+    protected bool $isFinal = false;
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct(array $config = [])
     {
         if (empty($config['type'])) {
@@ -37,15 +41,12 @@ public function __construct(array $config = [])
         $this->build($this->config);
     }
 
-    public function build(InputFieldConfig $config)
+    public function build(InputFieldConfig $config): void
     {
 
     }
 
-    /**
-     * @return InputTypeInterface
-     */
-    abstract public function getType();
+    abstract public function getType(): mixed;
 
     public function getDefaultValue()
     {
diff --git a/src/Field/Field.php b/src/Field/Field.php
index fd63b289..736de423 100644
--- a/src/Field/Field.php
+++ b/src/Field/Field.php
@@ -7,8 +7,6 @@
 
 namespace Youshido\GraphQL\Field;
 
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
-
 /**
  * Class Field
  * @package Youshido\GraphQL\Type\Field
@@ -17,22 +15,19 @@
 final class Field extends AbstractField
 {
 
-    protected $isFinal = true;
+    protected bool $isFinal = true;
+
+    protected $_typeCache;
 
-    protected $_typeCache = null;
-    protected $_nameCache = null;
+    protected $_nameCache;
 
-    /**
-     * @return AbstractObjectType
-     */
-    public function getType()
+    public function getType(): mixed
     {
-        return $this->_typeCache ? $this->_typeCache : ($this->_typeCache = $this->getConfigValue('type'));
+        return $this->_typeCache ?: ($this->_typeCache = $this->getConfigValue('type'));
     }
 
     public function getName()
     {
-        return $this->_nameCache ? $this->_nameCache : ($this->_nameCache = $this->getConfigValue('name'));
+        return $this->_nameCache ?: ($this->_nameCache = $this->getConfigValue('name'));
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Field/FieldInterface.php b/src/Field/FieldInterface.php
index edaac4ba..fbe5945c 100644
--- a/src/Field/FieldInterface.php
+++ b/src/Field/FieldInterface.php
@@ -12,7 +12,7 @@
 
 interface FieldInterface extends InputFieldInterface
 {
-    public function resolve($value, array $args, ResolveInfo $info);
+    public function resolve($value, array $args, ResolveInfo $info): mixed;
 
-    public function getResolveFunction();
+    public function getResolveFunction(): ?callable;
 }
diff --git a/src/Field/InputField.php b/src/Field/InputField.php
index 5bf34b70..c0aed6e5 100644
--- a/src/Field/InputField.php
+++ b/src/Field/InputField.php
@@ -9,17 +9,12 @@
 namespace Youshido\GraphQL\Field;
 
 
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
-
 final class InputField extends AbstractInputField
 {
 
-    protected $isFinal = false;
+    protected bool $isFinal = false;
 
-    /**
-     * @return AbstractObjectType
-     */
-    public function getType()
+    public function getType(): mixed
     {
         return $this->getConfigValue('type');
     }
diff --git a/src/Field/InputFieldInterface.php b/src/Field/InputFieldInterface.php
index d658c15c..13c79d7f 100644
--- a/src/Field/InputFieldInterface.php
+++ b/src/Field/InputFieldInterface.php
@@ -13,10 +13,7 @@
 
 interface InputFieldInterface
 {
-    /**
-     * @return AbstractType
-     */
-    public function getType();
+    public function getType(): mixed;
 
     public function getName();
 
@@ -29,26 +26,13 @@ public function addArgument($argument, $ArgumentInfo = null);
     /**
      * @return AbstractType[]
      */
-    public function getArguments();
+    public function getArguments(): array;
 
-    /**
-     * @param string $argumentName
-     *
-     * @return AbstractType
-     */
-    public function getArgument($argumentName);
+    public function getArgument(string $argumentName);
 
-    /**
-     * @param string $argumentName
-     *
-     * @return bool
-     */
-    public function hasArgument($argumentName);
+    public function hasArgument(string $argumentName): bool;
 
-    /**
-     * @return boolean
-     */
-    public function hasArguments();
+    public function hasArguments(): bool;
 
 
 }
diff --git a/src/Introspection/DirectiveLocationType.php b/src/Introspection/DirectiveLocationType.php
index d5b5e16f..8b2e3ba8 100644
--- a/src/Introspection/DirectiveLocationType.php
+++ b/src/Introspection/DirectiveLocationType.php
@@ -13,21 +13,28 @@
 class DirectiveLocationType extends AbstractEnumType
 {
 
-    const QUERY = DirectiveLocation::QUERY;
-    const MUTATION = DirectiveLocation::MUTATION;
-    const FIELD = DirectiveLocation::FIELD;
-    const FIELD_DEFINITION = DirectiveLocation::FIELD_DEFINITION;
-    const FRAGMENT_DEFINITION = DirectiveLocation::FRAGMENT_DEFINITION;
-    const FRAGMENT_SPREAD = DirectiveLocation::FRAGMENT_SPREAD;
-    const INLINE_FRAGMENT = DirectiveLocation::INLINE_FRAGMENT;
-    const ENUM_VALUE = DirectiveLocation::ENUM_VALUE;
-
-    public function getName()
+    final const QUERY = DirectiveLocation::QUERY;
+
+    final const MUTATION = DirectiveLocation::MUTATION;
+
+    final const FIELD = DirectiveLocation::FIELD;
+
+    final const FIELD_DEFINITION = DirectiveLocation::FIELD_DEFINITION;
+
+    final const FRAGMENT_DEFINITION = DirectiveLocation::FRAGMENT_DEFINITION;
+
+    final const FRAGMENT_SPREAD = DirectiveLocation::FRAGMENT_SPREAD;
+
+    final const INLINE_FRAGMENT = DirectiveLocation::INLINE_FRAGMENT;
+
+    final const ENUM_VALUE = DirectiveLocation::ENUM_VALUE;
+
+    public function getName(): string
     {
         return '__DirectiveLocation';
     }
 
-    public function getValues()
+    public function getValues(): array
     {
         return [
             ['name' => 'QUERY', 'value' => self::QUERY],
diff --git a/src/Introspection/DirectiveType.php b/src/Introspection/DirectiveType.php
index ba03632e..e4e49c1d 100644
--- a/src/Introspection/DirectiveType.php
+++ b/src/Introspection/DirectiveType.php
@@ -8,8 +8,9 @@
 namespace Youshido\GraphQL\Introspection;
 
 use Youshido\GraphQL\Config\Directive\DirectiveConfig;
-use Youshido\GraphQL\Directive\Directive;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Directive\DirectiveInterface;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\ListType\ListType;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
@@ -17,16 +18,15 @@
 
 class DirectiveType extends AbstractObjectType
 {
-
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__Directive';
     }
 
-    public function resolveArgs(DirectiveInterface $value)
+    public function resolveArgs(DirectiveInterface $value): array
     {
         if ($value->hasArguments()) {
             return $value->getArguments();
@@ -35,33 +35,29 @@ public function resolveArgs(DirectiveInterface $value)
         return [];
     }
 
-    /**
-     * @param DirectiveInterface|Directive $value
-     *
-     * @return mixed
-     */
-    public function resolveLocations(DirectiveInterface $value)
+    public function resolveLocations(DirectiveInterface $value): mixed
     {
         /** @var DirectiveConfig $directiveConfig */
         $directiveConfig = $value->getConfig();
 
-        $locations = $directiveConfig->getLocations();
-
-        return $locations;
+        return $directiveConfig->getLocations();
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('name', new NonNullType(TypeMap::TYPE_STRING))
             ->addField('description', TypeMap::TYPE_STRING)
             ->addField('args', [
-                'type'    => new NonNullType(new ListType(new NonNullType(new InputValueType()))),
-                'resolve' => [$this, 'resolveArgs'],
+                'type' => new NonNullType(new ListType(new NonNullType(new InputValueType()))),
+                'resolve' => $this->resolveArgs(...),
             ])
-            ->addField('locations',[
-                'type'  =>  new NonNullType(new ListType(new NonNullType(new DirectiveLocationType()))),
-                'resolve' => [$this, 'resolveLocations'],
+            ->addField('locations', [
+                'type' => new NonNullType(new ListType(new NonNullType(new DirectiveLocationType()))),
+                'resolve' => $this->resolveLocations(...),
             ]);
     }
 }
diff --git a/src/Introspection/EnumValueType.php b/src/Introspection/EnumValueType.php
index 823b85af..bfa5902b 100644
--- a/src/Introspection/EnumValueType.php
+++ b/src/Introspection/EnumValueType.php
@@ -8,6 +8,8 @@
 namespace Youshido\GraphQL\Introspection;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\TypeMap;
@@ -15,7 +17,10 @@
 class EnumValueType extends AbstractObjectType
 {
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('name', new NonNullType(TypeMap::TYPE_STRING))
@@ -27,7 +32,7 @@ public function build($config)
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__EnumValue';
     }
diff --git a/src/Introspection/Field/SchemaField.php b/src/Introspection/Field/SchemaField.php
index 5febedde..f89f4fba 100644
--- a/src/Introspection/Field/SchemaField.php
+++ b/src/Introspection/Field/SchemaField.php
@@ -11,27 +11,21 @@
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\AbstractField;
 use Youshido\GraphQL\Introspection\SchemaType;
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
 
 class SchemaField extends AbstractField
 {
-    /**
-     * @return AbstractObjectType
-     */
-    public function getType()
+    public function getType(): SchemaType
     {
         return new SchemaType();
     }
 
-    public function getName()
+    public function getName(): string
     {
         return '__schema';
     }
 
-    public function resolve($value, array $args, ResolveInfo $info)
+    public function resolve($value, array $args, ResolveInfo $info): mixed
     {
         return $info->getExecutionContext()->getSchema();
     }
-
-
 }
diff --git a/src/Introspection/Field/TypeDefinitionField.php b/src/Introspection/Field/TypeDefinitionField.php
index 4f0aae78..2c3e26ba 100644
--- a/src/Introspection/Field/TypeDefinitionField.php
+++ b/src/Introspection/Field/TypeDefinitionField.php
@@ -8,13 +8,13 @@
 namespace Youshido\GraphQL\Introspection\Field;
 
 use Youshido\GraphQL\Config\Field\FieldConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\AbstractField;
 use Youshido\GraphQL\Field\InputField;
 use Youshido\GraphQL\Introspection\QueryType;
 use Youshido\GraphQL\Introspection\Traits\TypeCollectorTrait;
 use Youshido\GraphQL\Type\NonNullType;
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\StringType;
 
 class TypeDefinitionField extends AbstractField
@@ -22,7 +22,7 @@ class TypeDefinitionField extends AbstractField
 
     use TypeCollectorTrait;
 
-    public function resolve($value, array $args, ResolveInfo $info)
+    public function resolve($value, array $args, ResolveInfo $info): mixed
     {
         $schema = $info->getExecutionContext()->getSchema();
         $this->collectTypes($schema->getQueryType());
@@ -41,7 +41,10 @@ public function resolve($value, array $args, ResolveInfo $info)
         return null;
     }
 
-    public function build(FieldConfig $config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(FieldConfig $config): void
     {
         $config->addArgument(new InputField([
             'name' => 'name',
@@ -53,15 +56,12 @@ public function build(FieldConfig $config)
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__type';
     }
 
-    /**
-     * @return AbstractObjectType
-     */
-    public function getType()
+    public function getType(): QueryType
     {
         return new QueryType();
     }
diff --git a/src/Introspection/Field/TypesField.php b/src/Introspection/Field/TypesField.php
index c0130338..54b08b5b 100644
--- a/src/Introspection/Field/TypesField.php
+++ b/src/Introspection/Field/TypesField.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Introspection\Field;
 
 
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\AbstractField;
 use Youshido\GraphQL\Introspection\QueryType;
@@ -23,18 +24,19 @@ class TypesField extends AbstractField
 
     /**
      * @return AbstractObjectType
+     * @throws ConfigurationException
      */
-    public function getType()
+    public function getType(): ListType
     {
         return new ListType(new QueryType());
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'types';
     }
 
-    public function resolve($value, array $args, ResolveInfo $info)
+    public function resolve($value, array $args, ResolveInfo $info): array
     {
         /** @var $value AbstractSchema $a */
         $this->types = [];
@@ -45,7 +47,7 @@ public function resolve($value, array $args, ResolveInfo $info)
         }
 
         foreach ($value->getTypesList()->getTypes() as $type) {
-          $this->collectTypes($type);
+            $this->collectTypes($type);
         }
 
         return array_values($this->types);
diff --git a/src/Introspection/FieldType.php b/src/Introspection/FieldType.php
index 81458c68..a47e4c46 100644
--- a/src/Introspection/FieldType.php
+++ b/src/Introspection/FieldType.php
@@ -7,7 +7,10 @@
 
 namespace Youshido\GraphQL\Introspection;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\FieldInterface;
+use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\ListType\ListType;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
@@ -16,12 +19,12 @@
 class FieldType extends AbstractObjectType
 {
 
-    public function resolveType(FieldInterface $value)
+    public function resolveType(FieldInterface $value): AbstractType
     {
         return $value->getType();
     }
 
-    public function resolveArgs(FieldInterface $value)
+    public function resolveArgs(FieldInterface $value): array
     {
         if ($value->hasArguments()) {
             return $value->getArguments();
@@ -30,7 +33,10 @@ public function resolveArgs(FieldInterface $value)
         return [];
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('name', new NonNullType(TypeMap::TYPE_STRING))
@@ -38,16 +44,16 @@ public function build($config)
             ->addField('isDeprecated', new NonNullType(TypeMap::TYPE_BOOLEAN))
             ->addField('deprecationReason', TypeMap::TYPE_STRING)
             ->addField('type', [
-                'type'    => new NonNullType(new QueryType()),
-                'resolve' => [$this, 'resolveType'],
+                'type' => new NonNullType(new QueryType()),
+                'resolve' => $this->resolveType(...),
             ])
             ->addField('args', [
-                'type'    => new NonNullType(new ListType(new NonNullType(new InputValueType()))),
-                'resolve' => [$this, 'resolveArgs'],
+                'type' => new NonNullType(new ListType(new NonNullType(new InputValueType()))),
+                'resolve' => $this->resolveArgs(...),
             ]);
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return $value instanceof FieldInterface;
     }
@@ -55,7 +61,7 @@ public function isValidValue($value)
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__Field';
     }
diff --git a/src/Introspection/InputValueType.php b/src/Introspection/InputValueType.php
index d2619a6a..a4e00ccc 100644
--- a/src/Introspection/InputValueType.php
+++ b/src/Introspection/InputValueType.php
@@ -7,7 +7,10 @@
 
 namespace Youshido\GraphQL\Introspection;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\Field;
+use Youshido\GraphQL\Field\InputField;
 use Youshido\GraphQL\Schema\AbstractSchema;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
@@ -16,30 +19,26 @@
 
 class InputValueType extends AbstractObjectType
 {
-    /**
-     * @param AbstractSchema|Field $value
-     *
-     * @return TypeInterface
-     */
-    public function resolveType($value)
+    public function resolveType(InputField|AbstractSchema|Field $value): TypeInterface
     {
         return $value->getConfig()->getType();
     }
 
     /**
-     * @param AbstractSchema|Field $value
-     *
-     * @return string|null
+     * @return string|array|null
      *
      * //todo implement value printer
      */
-    public function resolveDefaultValue($value)
+    public function resolveDefaultValue(InputField|AbstractSchema|Field $value): string|array|null
     {
         $resolvedValue = $value->getConfig()->getDefaultValue();
         return $resolvedValue === null ? $resolvedValue : str_replace('"', '', json_encode($resolvedValue));
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('name', new NonNullType(TypeMap::TYPE_STRING))
@@ -47,21 +46,21 @@ public function build($config)
             ->addField('isDeprecated', new NonNullType(TypeMap::TYPE_BOOLEAN))
             ->addField('deprecationReason', TypeMap::TYPE_STRING)
             ->addField(new Field([
-                'name'    => 'type',
-                'type'    => new NonNullType(new QueryType()),
-                'resolve' => [$this, 'resolveType']
+                'name' => 'type',
+                'type' => new NonNullType(new QueryType()),
+                'resolve' => $this->resolveType(...)
             ]))
             ->addField('defaultValue', [
                 'type' => TypeMap::TYPE_STRING,
-                'resolve' => [$this, 'resolveDefaultValue']
+                'resolve' => $this->resolveDefaultValue(...)
             ]);
     }
 
     /**
      * @return string type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__InputValue';
     }
-}
+}
\ No newline at end of file
diff --git a/src/Introspection/QueryType.php b/src/Introspection/QueryType.php
index 0de0bfc8..a4b80143 100644
--- a/src/Introspection/QueryType.php
+++ b/src/Introspection/QueryType.php
@@ -7,6 +7,8 @@
 
 namespace Youshido\GraphQL\Introspection;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Introspection\Traits\TypeCollectorTrait;
@@ -21,6 +23,7 @@
 use Youshido\GraphQL\Type\Scalar\BooleanType;
 use Youshido\GraphQL\Type\TypeMap;
 use Youshido\GraphQL\Type\Union\AbstractUnionType;
+use function array_unique;
 
 class QueryType extends AbstractObjectType
 {
@@ -30,7 +33,7 @@ class QueryType extends AbstractObjectType
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__Type';
     }
@@ -44,7 +47,7 @@ public function resolveOfType(AbstractType $value)
         return null;
     }
 
-    public function resolveInputFields($value)
+    public function resolveInputFields($value): ?array
     {
         if ($value instanceof AbstractInputObjectType) {
             /** @var AbstractObjectType $value */
@@ -54,22 +57,24 @@ public function resolveInputFields($value)
         return null;
     }
 
-    public function resolveEnumValues($value, $args)
+    public function resolveEnumValues($value, array $args): ?array
     {
         /** @var $value AbstractType|AbstractEnumType */
         if ($value && $value->getKind() == TypeMap::KIND_ENUM) {
             $data = [];
             foreach ($value->getValues() as $enumValue) {
-                if(!$args['includeDeprecated'] && (isset($enumValue['isDeprecated']) && $enumValue['isDeprecated'])) {
+                if (!$args['includeDeprecated'] && (isset($enumValue['isDeprecated']) && $enumValue['isDeprecated'])) {
                     continue;
                 }
 
                 if (!array_key_exists('description', $enumValue)) {
                     $enumValue['description'] = '';
                 }
+
                 if (!array_key_exists('isDeprecated', $enumValue)) {
                     $enumValue['isDeprecated'] = false;
                 }
+
                 if (!array_key_exists('deprecationReason', $enumValue)) {
                     $enumValue['deprecationReason'] = null;
                 }
@@ -83,7 +88,7 @@ public function resolveEnumValues($value, $args)
         return null;
     }
 
-    public function resolveFields($value, $args)
+    public function resolveFields($value, $args): ?array
     {
         /** @var AbstractType $value */
         if (!$value ||
@@ -93,17 +98,13 @@ public function resolveFields($value, $args)
         }
 
         /** @var AbstractObjectType $value */
-        return array_filter($value->getConfig()->getFields(), function ($field) use ($args) {
+        return array_filter($value->getConfig()->getFields(), static function ($field) use ($args): bool {
             /** @var $field Field */
-            if (in_array($field->getName(), ['__type', '__schema']) || (!$args['includeDeprecated'] && $field->isDeprecated())) {
-                return false;
-            }
-
-            return true;
+            return !in_array($field->getName(), ['__type', '__schema']) && !(!$args['includeDeprecated'] && $field->isDeprecated());
         });
     }
 
-    public function resolveInterfaces($value)
+    public function resolveInterfaces($value): array
     {
         /** @var $value AbstractType */
         if ($value->getKind() == TypeMap::KIND_OBJECT) {
@@ -111,17 +112,17 @@ public function resolveInterfaces($value)
             return $value->getConfig()->getInterfaces() ?: [];
         }
 
-        return null;
+        return [];
     }
 
-    public function resolvePossibleTypes($value, $args, ResolveInfo $info)
+    public function resolvePossibleTypes($value, $args, ResolveInfo $info): ?array
     {
         /** @var $value AbstractObjectType */
         if ($value->getKind() == TypeMap::KIND_INTERFACE) {
             $schema = $info->getExecutionContext()->getSchema();
             $this->collectTypes($schema->getQueryType());
             foreach ($schema->getTypesList()->getTypes() as $type) {
-              $this->collectTypes($type);
+                $this->collectTypes($type);
             }
 
             $possibleTypes = [];
@@ -146,7 +147,7 @@ public function resolvePossibleTypes($value, $args, ResolveInfo $info)
                 }
             }
 
-            return \array_unique($possibleTypes);
+            return array_unique($possibleTypes);
         } elseif ($value->getKind() == TypeMap::KIND_UNION) {
             /** @var $value AbstractUnionType */
             return $value->getTypes();
@@ -155,52 +156,60 @@ public function resolvePossibleTypes($value, $args, ResolveInfo $info)
         return null;
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('name', TypeMap::TYPE_STRING)
             ->addField('kind', new NonNullType(TypeMap::TYPE_STRING))
             ->addField('description', TypeMap::TYPE_STRING)
             ->addField('ofType', [
-                'type'    => new QueryType(),
-                'resolve' => [$this, 'resolveOfType']
+                'type' => new QueryType(),
+                'resolve' => $this->resolveOfType(...)
             ])
             ->addField(new Field([
-                'name'    => 'inputFields',
-                'type'    => new ListType(new NonNullType(new InputValueType())),
-                'resolve' => [$this, 'resolveInputFields']
+                'name' => 'inputFields',
+                'type' => new ListType(new NonNullType(new InputValueType())),
+                'resolve' => $this->resolveInputFields(...)
             ]))
             ->addField(new Field([
-                'name'    => 'enumValues',
-                'args'    => [
+                'name' => 'enumValues',
+                'args' => [
                     'includeDeprecated' => [
-                        'type'    => new BooleanType(),
+                        'type' => new BooleanType(),
                         'defaultValue' => false
                     ]
                 ],
-                'type'    => new ListType(new NonNullType(new EnumValueType())),
-                'resolve' => [$this, 'resolveEnumValues']
+                'type' => new ListType(new NonNullType(new EnumValueType())),
+                'resolve' => function ($value, array $args): ?array {
+                    return $this->resolveEnumValues($value, $args);
+                }
             ]))
             ->addField(new Field([
-                'name'    => 'fields',
-                'args'    => [
+                'name' => 'fields',
+                'args' => [
                     'includeDeprecated' => [
-                        'type'    => new BooleanType(),
+                        'type' => new BooleanType(),
                         'defaultValue' => false
                     ]
                 ],
-                'type'    => new ListType(new NonNullType(new FieldType())),
-                'resolve' => [$this, 'resolveFields']
+                'type' => new ListType(new NonNullType(new FieldType())),
+                'resolve' => function ($value, $args): ?array {
+                    return $this->resolveFields($value, $args);
+                }
             ]))
             ->addField(new Field([
-                'name'    => 'interfaces',
-                'type'    => new ListType(new NonNullType(new QueryType())),
-                'resolve' => [$this, 'resolveInterfaces']
+                'name' => 'interfaces',
+                'type' => new ListType(new NonNullType(new QueryType())),
+                'resolve' => $this->resolveInterfaces(...)
             ]))
             ->addField('possibleTypes', [
-                'type'    => new ListType(new NonNullType(new QueryType())),
-                'resolve' => [$this, 'resolvePossibleTypes']
+                'type' => new ListType(new NonNullType(new QueryType())),
+                'resolve' => function ($value, $args, ResolveInfo $info): ?array {
+                    return $this->resolvePossibleTypes($value, $args, $info);
+                }
             ]);
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Introspection/SchemaType.php b/src/Introspection/SchemaType.php
index 3065a218..c3889e68 100644
--- a/src/Introspection/SchemaType.php
+++ b/src/Introspection/SchemaType.php
@@ -7,6 +7,8 @@
 
 namespace Youshido\GraphQL\Introspection;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Introspection\Field\TypesField;
 use Youshido\GraphQL\Schema\AbstractSchema;
@@ -19,7 +21,7 @@ class SchemaType extends AbstractObjectType
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return '__Schema';
     }
@@ -41,36 +43,38 @@ public function resolveSubscriptionType()
         return null;
     }
 
-    public function resolveDirectives($value)
+    public function resolveDirectives($value): array
     {
         /** @var AbstractSchema|Field $value */
-        $dirs = $value->getDirectiveList()->getDirectives();
-        return $dirs;
+        return $value->getDirectiveList()->getDirectives();
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField(new Field([
-                'name'    => 'queryType',
-                'type'    => new QueryType(),
-                'resolve' => [$this, 'resolveQueryType']
+                'name' => 'queryType',
+                'type' => new QueryType(),
+                'resolve' => $this->resolveQueryType(...)
             ]))
             ->addField(new Field([
-                'name'    => 'mutationType',
-                'type'    => new QueryType(),
-                'resolve' => [$this, 'resolveMutationType']
+                'name' => 'mutationType',
+                'type' => new QueryType(),
+                'resolve' => $this->resolveMutationType(...)
             ]))
             ->addField(new Field([
-                'name'    => 'subscriptionType',
-                'type'    => new QueryType(),
-                'resolve' => [$this, 'resolveSubscriptionType']
+                'name' => 'subscriptionType',
+                'type' => new QueryType(),
+                'resolve' => $this->resolveSubscriptionType(...)
             ]))
             ->addField(new TypesField())
             ->addField(new Field([
-                'name'    => 'directives',
-                'type'    => new ListType(new DirectiveType()),
-                'resolve' => [$this, 'resolveDirectives']
+                'name' => 'directives',
+                'type' => new ListType(new DirectiveType()),
+                'resolve' => $this->resolveDirectives(...)
             ]));
     }
 }
diff --git a/src/Introspection/Traits/TypeCollectorTrait.php b/src/Introspection/Traits/TypeCollectorTrait.php
index 7390285c..7d4ee4a0 100644
--- a/src/Introspection/Traits/TypeCollectorTrait.php
+++ b/src/Introspection/Traits/TypeCollectorTrait.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Introspection\Traits;
 
 use Youshido\GraphQL\Type\AbstractType;
+use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\TypeMap;
@@ -15,12 +16,13 @@
 
 trait TypeCollectorTrait
 {
+    protected array $types = [];
 
-    protected $types = [];
-
-    protected function collectTypes(AbstractType $type)
+    protected function collectTypes(?AbstractType $type): void
     {
-        if (is_object($type) && array_key_exists($type->getName(), $this->types)) return;
+        if (!$type instanceof AbstractType || array_key_exists($type->getName(), $this->types)) {
+            return;
+        }
 
         switch ($type->getKind()) {
             case TypeMap::KIND_INTERFACE:
@@ -29,7 +31,7 @@ protected function collectTypes(AbstractType $type)
             case TypeMap::KIND_SCALAR:
                 $this->insertType($type->getName(), $type);
 
-                if ($type->getKind() == TypeMap::KIND_UNION) {
+                if ($type->getKind() === TypeMap::KIND_UNION) {
                     /** @var AbstractUnionType $type */
                     foreach ($type->getTypes() as $subType) {
                         $this->collectTypes($subType);
@@ -51,8 +53,6 @@ protected function collectTypes(AbstractType $type)
                 break;
 
             case TypeMap::KIND_LIST:
-                $this->collectTypes($type->getNamedType());
-                break;
 
             case TypeMap::KIND_NON_NULL:
                 $this->collectTypes($type->getNamedType());
@@ -61,7 +61,7 @@ protected function collectTypes(AbstractType $type)
         }
     }
 
-    private function checkAndInsertInterfaces($type)
+    private function checkAndInsertInterfaces($type): void
     {
         foreach ((array)$type->getConfig()->getInterfaces() as $interface) {
             $this->insertType($interface->getName(), $interface);
@@ -74,10 +74,7 @@ private function checkAndInsertInterfaces($type)
         }
     }
 
-    /**
-     * @param $type AbstractObjectType
-     */
-    private function collectFieldsArgsTypes($type)
+    private function collectFieldsArgsTypes(AbstractObjectType|AbstractInputObjectType $type): void
     {
         foreach ($type->getConfig()->getFields() as $field) {
             $arguments = $field->getConfig()->getArguments();
@@ -92,7 +89,7 @@ private function collectFieldsArgsTypes($type)
         }
     }
 
-    private function insertType($name, $type)
+    private function insertType($name, $type): bool
     {
         if (!array_key_exists($name, $this->types)) {
             $this->types[$name] = $type;
@@ -102,5 +99,4 @@ private function insertType($name, $type)
 
         return false;
     }
-
 }
diff --git a/src/Parser/Ast/AbstractAst.php b/src/Parser/Ast/AbstractAst.php
index 7f7dce3d..e9fc2a7d 100644
--- a/src/Parser/Ast/AbstractAst.php
+++ b/src/Parser/Ast/AbstractAst.php
@@ -14,8 +14,7 @@
 abstract class AbstractAst implements LocatableInterface
 {
 
-    /** @var  Location */
-    private $location;
+    private Location $location;
 
     public function __construct(Location $location)
     {
@@ -27,7 +26,7 @@ public function getLocation()
         return $this->location;
     }
 
-    public function setLocation(Location $location)
+    public function setLocation(Location $location): void
     {
         $this->location = $location;
     }
diff --git a/src/Parser/Ast/Argument.php b/src/Parser/Ast/Argument.php
index bb0aa8af..f31c2f59 100644
--- a/src/Parser/Ast/Argument.php
+++ b/src/Parser/Ast/Argument.php
@@ -7,63 +7,46 @@
 
 namespace Youshido\GraphQL\Parser\Ast;
 
-
 use Youshido\GraphQL\Parser\Ast\Interfaces\ValueInterface;
 use Youshido\GraphQL\Parser\Location;
 
-class Argument extends AbstractAst
+class Argument extends AbstractAst implements ValueInterface
 {
+    private string $name;
 
-    /** @var string */
-    private $name;
-
-    /** @var ValueInterface */
-    private $value;
+    /**
+     * TODO - Was ValueInterface - is there any reason for that?
+     */
+    private mixed $value;
 
     /**
-     * @param string         $name
-     * @param ValueInterface $value
-     * @param Location       $location
+     * @param string $name
      */
-    public function __construct($name, ValueInterface $value, Location $location)
+    public function __construct($name, $value, Location $location)
     {
         parent::__construct($location);
 
-        $this->name  = $name;
+        $this->name = $name;
         $this->value = $value;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
 
-    /**
-     * @param mixed $name
-     */
-    public function setName($name)
+    public function setName(string $name): void
     {
         $this->name = $name;
     }
 
-    /**
-     * @return \Youshido\GraphQL\Parser\Ast\Interfaces\ValueInterface
-     */
-    public function getValue()
+    public function getValue(): mixed
     {
         return $this->value;
     }
 
-    /**
-     * @param mixed $value
-     */
-    public function setValue($value)
+    public function setValue(mixed $value): void
     {
         $this->value = $value;
     }
-
-
 }
\ No newline at end of file
diff --git a/src/Parser/Ast/ArgumentValue/InputList.php b/src/Parser/Ast/ArgumentValue/InputList.php
index 03867885..4c3b7247 100644
--- a/src/Parser/Ast/ArgumentValue/InputList.php
+++ b/src/Parser/Ast/ArgumentValue/InputList.php
@@ -15,12 +15,8 @@
 class InputList extends AbstractAst implements ValueInterface
 {
 
-    protected $list = [];
+    protected array $list;
 
-    /**
-     * @param array    $list
-     * @param Location $location
-     */
     public function __construct(array $list, Location $location)
     {
         parent::__construct($location);
@@ -28,10 +24,7 @@ public function __construct(array $list, Location $location)
         $this->list = $list;
     }
 
-    /**
-     * @return array
-     */
-    public function getValue()
+    public function getValue(): array
     {
         return $this->list;
     }
@@ -39,7 +32,7 @@ public function getValue()
     /**
      * @param array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->list = $value;
     }
diff --git a/src/Parser/Ast/ArgumentValue/InputObject.php b/src/Parser/Ast/ArgumentValue/InputObject.php
index 92b34144..7b900ab6 100644
--- a/src/Parser/Ast/ArgumentValue/InputObject.php
+++ b/src/Parser/Ast/ArgumentValue/InputObject.php
@@ -15,12 +15,8 @@
 class InputObject extends AbstractAst implements ValueInterface
 {
 
-    protected $object = [];
+    protected array $object;
 
-    /**
-     * @param array    $object
-     * @param Location $location
-     */
     public function __construct(array $object, Location $location)
     {
         parent::__construct($location);
@@ -28,10 +24,7 @@ public function __construct(array $object, Location $location)
         $this->object = $object;
     }
 
-    /**
-     * @return array
-     */
-    public function getValue()
+    public function getValue(): array
     {
         return $this->object;
     }
@@ -39,7 +32,7 @@ public function getValue()
     /**
      * @param array $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->object = $value;
     }
diff --git a/src/Parser/Ast/ArgumentValue/Literal.php b/src/Parser/Ast/ArgumentValue/Literal.php
index dabd6319..9b885745 100644
--- a/src/Parser/Ast/ArgumentValue/Literal.php
+++ b/src/Parser/Ast/ArgumentValue/Literal.php
@@ -19,7 +19,6 @@ class Literal extends AbstractAst implements ValueInterface
 
     /**
      * @param mixed $value
-     * @param Location $location
      */
     public function __construct($value, Location $location)
     {
@@ -36,7 +35,7 @@ public function getValue()
     /**
      * @param string $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->value = $value;
     }
diff --git a/src/Parser/Ast/ArgumentValue/Variable.php b/src/Parser/Ast/ArgumentValue/Variable.php
index 63b9d01d..01203d89 100644
--- a/src/Parser/Ast/ArgumentValue/Variable.php
+++ b/src/Parser/Ast/ArgumentValue/Variable.php
@@ -7,6 +7,7 @@
 
 namespace Youshido\GraphQL\Parser\Ast\ArgumentValue;
 
+use LogicException;
 use Youshido\GraphQL\Parser\Ast\AbstractAst;
 use Youshido\GraphQL\Parser\Ast\Interfaces\ValueInterface;
 use Youshido\GraphQL\Parser\Location;
@@ -23,47 +24,41 @@ class Variable extends AbstractAst implements ValueInterface
     /** @var string */
     private $type;
 
-    /** @var bool */
-    private $nullable = false;
+    private bool $nullable = false;
 
-    /** @var bool */
-    private $isArray = false;
+    private bool $isArray = false;
 
-    /** @var bool */
-    private $used = false;
+    private bool $used = false;
 
-    /** @var bool */
-    private $arrayElementNullable = true;
+    private bool $arrayElementNullable = true;
 
-    /** @var bool */
-    private $hasDefaultValue = false;
+    private bool $hasDefaultValue = false;
 
     /** @var mixed */
-    private $defaultValue = null;
+    private $defaultValue;
 
     /**
-     * @param string   $name
-     * @param string   $type
-     * @param bool     $nullable
-     * @param bool     $isArray
-     * @param bool     $arrayElementNullable
-     * @param Location $location
+     * @param string $name
+     * @param string $type
+     * @param bool $nullable
+     * @param bool $isArray
+     * @param bool $arrayElementNullable
      */
-    public function __construct($name, $type, $nullable, $isArray, $arrayElementNullable = true, Location $location)
+    public function __construct($name, $type, $nullable, $isArray, Location $location, $arrayElementNullable = true)
     {
         parent::__construct($location);
 
-        $this->name                 = $name;
-        $this->type                 = $type;
-        $this->isArray              = $isArray;
-        $this->nullable             = $nullable;
+        $this->name = $name;
+        $this->type = $type;
+        $this->isArray = $isArray;
+        $this->nullable = $nullable;
         $this->arrayElementNullable = $arrayElementNullable;
     }
 
     /**
      * @return mixed
      *
-     * @throws \LogicException
+     * @throws LogicException
      */
     public function getValue()
     {
@@ -71,7 +66,8 @@ public function getValue()
             if ($this->hasDefaultValue()) {
                 return $this->defaultValue;
             }
-            throw new \LogicException('Value is not set for variable "' . $this->name . '"');
+
+            throw new LogicException('Value is not set for variable "' . $this->name . '"');
         }
 
         return $this->value;
@@ -80,7 +76,7 @@ public function getValue()
     /**
      * @param mixed $value
      */
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->value = $value;
     }
@@ -96,7 +92,7 @@ public function getName()
     /**
      * @param string $name
      */
-    public function setName($name)
+    public function setName($name): void
     {
         $this->name = $name;
     }
@@ -112,47 +108,32 @@ public function getTypeName()
     /**
      * @param string $type
      */
-    public function setTypeName($type)
+    public function setTypeName($type): void
     {
         $this->type = $type;
     }
 
-    /**
-     * @return boolean
-     */
-    public function isArray()
+    public function isArray(): bool
     {
         return $this->isArray;
     }
 
-    /**
-     * @param boolean $isArray
-     */
-    public function setIsArray($isArray)
+    public function setIsArray(bool $isArray): void
     {
         $this->isArray = $isArray;
     }
 
-    /**
-     * @return boolean
-     */
-    public function isNullable()
+    public function isNullable(): bool
     {
         return $this->nullable;
     }
 
-    /**
-     * @param boolean $nullable
-     */
-    public function setNullable($nullable)
+    public function setNullable(bool $nullable): void
     {
         $this->nullable = $nullable;
     }
 
-    /**
-     * @return bool
-     */
-    public function hasDefaultValue()
+    public function hasDefaultValue(): bool
     {
         return $this->hasDefaultValue;
     }
@@ -168,45 +149,34 @@ public function getDefaultValue()
     /**
      * @param mixed $defaultValue
      */
-    public function setDefaultValue($defaultValue)
+    public function setDefaultValue($defaultValue): void
     {
         $this->hasDefaultValue = true;
 
         $this->defaultValue = $defaultValue;
     }
 
-    /**
-     * @return boolean
-     */
-    public function isUsed()
+    public function isUsed(): bool
     {
         return $this->used;
     }
 
     /**
-     * @param boolean $used
-     *
      * @return $this
      */
-    public function setUsed($used)
+    public function setUsed(bool $used): static
     {
         $this->used = $used;
 
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isArrayElementNullable()
+    public function isArrayElementNullable(): bool
     {
         return $this->arrayElementNullable;
     }
 
-    /**
-     * @param bool $arrayElementNullable
-     */
-    public function setArrayElementNullable($arrayElementNullable)
+    public function setArrayElementNullable(bool $arrayElementNullable): void
     {
         $this->arrayElementNullable = $arrayElementNullable;
     }
diff --git a/src/Parser/Ast/ArgumentValue/VariableReference.php b/src/Parser/Ast/ArgumentValue/VariableReference.php
index c754db1d..dac879cb 100644
--- a/src/Parser/Ast/ArgumentValue/VariableReference.php
+++ b/src/Parser/Ast/ArgumentValue/VariableReference.php
@@ -18,26 +18,24 @@ class VariableReference extends AbstractAst implements ValueInterface
     /** @var  string */
     private $name;
 
-    /** @var  Variable */
-    private $variable;
+    private readonly ?Variable $variable;
 
     /** @var  mixed */
     private $value;
 
     /**
-     * @param string        $name
+     * @param string $name
      * @param Variable|null $variable
-     * @param Location      $location
      */
-    public function __construct($name, Variable $variable = null, Location $location)
+    public function __construct($name, Location $location, ?Variable $variable = null)
     {
         parent::__construct($location);
 
-        $this->name     = $name;
+        $this->name = $name;
         $this->variable = $variable;
     }
 
-    public function getVariable()
+    public function getVariable(): ?Variable
     {
         return $this->variable;
     }
@@ -47,7 +45,7 @@ public function getValue()
         return $this->value;
     }
 
-    public function setValue($value)
+    public function setValue($value): void
     {
         $this->value = $value;
     }
diff --git a/src/Parser/Ast/AstArgumentsTrait.php b/src/Parser/Ast/AstArgumentsTrait.php
index b572b3a7..dfe38bf7 100644
--- a/src/Parser/Ast/AstArgumentsTrait.php
+++ b/src/Parser/Ast/AstArgumentsTrait.php
@@ -13,17 +13,17 @@ trait AstArgumentsTrait
 {
 
     /** @var Argument[] */
-    protected $arguments;
+    protected array $arguments;
 
-    private $argumentsCache = null;
+    private $argumentsCache;
 
 
-    public function hasArguments()
+    public function hasArguments(): bool
     {
         return (bool)count($this->arguments);
     }
 
-    public function hasArgument($name)
+    public function hasArgument($name): bool
     {
         return array_key_exists($name, $this->arguments);
     }
@@ -31,17 +31,12 @@ public function hasArgument($name)
     /**
      * @return Argument[]
      */
-    public function getArguments()
+    public function getArguments(): array
     {
         return $this->arguments;
     }
 
-    /**
-     * @param $name
-     *
-     * @return null|Argument
-     */
-    public function getArgument($name)
+    public function getArgument(string $name): ?Argument
     {
         $argument = null;
         if (isset($this->arguments[$name])) {
@@ -55,13 +50,13 @@ public function getArgumentValue($name)
     {
         $argument = $this->getArgument($name);
 
-        return $argument ? $argument->getValue()->getValue() : null;
+        return $argument?->getValue()->getValue();
     }
 
     /**
      * @param $arguments Argument[]
      */
-    public function setArguments(array $arguments)
+    public function setArguments(array $arguments): void
     {
         $this->arguments = [];
         $this->argumentsCache = null;
@@ -71,12 +66,12 @@ public function setArguments(array $arguments)
         }
     }
 
-    public function addArgument(Argument $argument)
+    public function addArgument(Argument $argument): void
     {
         $this->arguments[$argument->getName()] = $argument;
     }
 
-    public function getKeyValueArguments()
+    public function getKeyValueArguments(): array
     {
         if ($this->argumentsCache !== null) {
             return $this->argumentsCache;
diff --git a/src/Parser/Ast/AstDirectivesTrait.php b/src/Parser/Ast/AstDirectivesTrait.php
index a4b37004..914fab4d 100644
--- a/src/Parser/Ast/AstDirectivesTrait.php
+++ b/src/Parser/Ast/AstDirectivesTrait.php
@@ -14,15 +14,15 @@ trait AstDirectivesTrait
     /** @var Directive[] */
     protected $directives;
 
-    private $directivesCache = null;
+    private $directivesCache;
 
 
-    public function hasDirectives()
+    public function hasDirectives(): bool
     {
         return (bool)count($this->directives);
     }
 
-    public function hasDirective($name)
+    public function hasDirective($name): bool
     {
         return array_key_exists($name, $this->directives);
     }
@@ -53,9 +53,9 @@ public function getDirectives()
     /**
      * @param $directives Directive[]
      */
-    public function setDirectives(array $directives)
+    public function setDirectives(array $directives): void
     {
-        $this->directives      = [];
+        $this->directives = [];
         $this->directivesCache = null;
 
         foreach ($directives as $directive) {
@@ -63,7 +63,7 @@ public function setDirectives(array $directives)
         }
     }
 
-    public function addDirective(Directive $directive)
+    public function addDirective(Directive $directive): void
     {
         $this->directives[$directive->getName()] = $directive;
     }
diff --git a/src/Parser/Ast/Directive.php b/src/Parser/Ast/Directive.php
index 9f66549b..647c6912 100644
--- a/src/Parser/Ast/Directive.php
+++ b/src/Parser/Ast/Directive.php
@@ -19,9 +19,7 @@ class Directive extends AbstractAst
 
 
     /**
-     * @param string   $name
-     * @param array    $arguments
-     * @param Location $location
+     * @param string $name
      */
     public function __construct($name, array $arguments, Location $location)
     {
@@ -42,7 +40,7 @@ public function getName()
     /**
      * @param mixed $name
      */
-    public function setName($name)
+    public function setName($name): void
     {
         $this->name = $name;
     }
diff --git a/src/Parser/Ast/Field.php b/src/Parser/Ast/Field.php
index 5036a171..fa8f2809 100644
--- a/src/Parser/Ast/Field.php
+++ b/src/Parser/Ast/Field.php
@@ -16,67 +16,50 @@ class Field extends AbstractAst implements FieldInterface
     use AstArgumentsTrait;
     use AstDirectivesTrait;
 
-    /** @var string */
-    private $name;
+    private ?string $name;
 
-    /** @var string */
-    private $alias;
+    private ?string $alias;
 
     /**
-     * @param string   $name
-     * @param string   $alias
-     * @param array    $arguments
-     * @param array    $directives
-     * @param Location $location
+     * @param string $name
+     * @param string $alias
      */
     public function __construct($name, $alias, array $arguments, array $directives, Location $location)
     {
         parent::__construct($location);
 
-        $this->name      = $name;
-        $this->alias     = $alias;
+        $this->name = $name;
+        $this->alias = $alias;
         $this->setArguments($arguments);
         $this->setDirectives($directives);
     }
 
-    /**
-     * @return string
-     */
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
 
-    /**
-     * @param string $name
-     */
-    public function setName($name)
+    public function setName(string $name): void
     {
         $this->name = $name;
     }
 
-    /**
-     * @return null|string
-     */
-    public function getAlias()
+    public function getAlias(): ?string
     {
         return $this->alias;
     }
 
-    /**
-     * @param null|string $alias
-     */
-    public function setAlias($alias)
+    public function setAlias(?string $alias): void
     {
         $this->alias = $alias;
     }
 
-    public function hasFields()
+    public function hasFields(): bool
     {
         return false;
     }
 
-    public function getFields()
+    public function getFields(): array
     {
         return [];
     }
diff --git a/src/Parser/Ast/Fragment.php b/src/Parser/Ast/Fragment.php
index 7ea8b142..3b10ad36 100644
--- a/src/Parser/Ast/Fragment.php
+++ b/src/Parser/Ast/Fragment.php
@@ -20,40 +20,31 @@ class Fragment extends AbstractAst
     protected $model;
 
     /** @var Field[]|Query[] */
-    protected $fields;
+    protected array $fields;
 
-    /** @var bool */
-    private $used = false;
+    private bool $used = false;
 
     /**
-     * @param string          $name
-     * @param string          $model
-     * @param array           $directives
+     * @param string $name
+     * @param string $model
      * @param Field[]|Query[] $fields
-     * @param Location        $location
      */
     public function __construct($name, $model, array $directives, array $fields, Location $location)
     {
         parent::__construct($location);
 
-        $this->name   = $name;
-        $this->model  = $model;
+        $this->name = $name;
+        $this->model = $model;
         $this->fields = $fields;
         $this->setDirectives($directives);
     }
 
-    /**
-     * @return boolean
-     */
-    public function isUsed()
+    public function isUsed(): bool
     {
         return $this->used;
     }
 
-    /**
-     * @param boolean $used
-     */
-    public function setUsed($used)
+    public function setUsed(bool $used): void
     {
         $this->used = $used;
     }
@@ -69,7 +60,7 @@ public function getName()
     /**
      * @param mixed $name
      */
-    public function setName($name)
+    public function setName($name): void
     {
         $this->name = $name;
     }
@@ -85,7 +76,7 @@ public function getModel()
     /**
      * @param mixed $model
      */
-    public function setModel($model)
+    public function setModel($model): void
     {
         $this->model = $model;
     }
@@ -93,7 +84,7 @@ public function setModel($model)
     /**
      * @return Field[]|Query[]
      */
-    public function getFields()
+    public function getFields(): array
     {
         return $this->fields;
     }
@@ -101,7 +92,7 @@ public function getFields()
     /**
      * @param Field[]|Query[] $fields
      */
-    public function setFields($fields)
+    public function setFields(array $fields): void
     {
         $this->fields = $fields;
     }
diff --git a/src/Parser/Ast/FragmentReference.php b/src/Parser/Ast/FragmentReference.php
index 1fa01083..87f9ff38 100644
--- a/src/Parser/Ast/FragmentReference.php
+++ b/src/Parser/Ast/FragmentReference.php
@@ -18,8 +18,7 @@ class FragmentReference extends AbstractAst implements FragmentInterface
     protected $name;
 
     /**
-     * @param string   $name
-     * @param Location $location
+     * @param string $name
      */
     public function __construct($name, Location $location)
     {
@@ -39,7 +38,7 @@ public function getName()
     /**
      * @param string $name
      */
-    public function setName($name)
+    public function setName($name): void
     {
         $this->name = $name;
     }
diff --git a/src/Parser/Ast/Interfaces/FieldInterface.php b/src/Parser/Ast/Interfaces/FieldInterface.php
index 2bc94bed..2737e913 100644
--- a/src/Parser/Ast/Interfaces/FieldInterface.php
+++ b/src/Parser/Ast/Interfaces/FieldInterface.php
@@ -12,37 +12,19 @@
 
 interface FieldInterface extends LocatableInterface
 {
+    public function getName(): string;
 
-    /**
-     * @return string
-     */
-    public function getName();
-
-    /**
-     * @return string
-     */
-    public function getAlias();
+    public function getAlias(): ?string;
 
     /**
      * @return Argument[]
      */
-    public function getArguments();
+    public function getArguments(): array;
 
-    /**
-     * @param string $name
-     *
-     * @return Argument
-     */
-    public function getArgument($name);
+    public function getArgument(string $name);
 
-    /**
-     * @return bool
-     */
-    public function hasFields();
+    public function hasFields(): bool;
 
-    /**
-     * @return array
-     */
-    public function getFields();
+    public function getFields(): array;
 
 }
diff --git a/src/Parser/Ast/Query.php b/src/Parser/Ast/Query.php
index 2feecd29..c6d31b4b 100644
--- a/src/Parser/Ast/Query.php
+++ b/src/Parser/Ast/Query.php
@@ -29,25 +29,21 @@ class Query extends AbstractAst implements FieldInterface
     /**
      * Query constructor.
      *
-     * @param string   $name
-     * @param string   $alias
-     * @param array    $arguments
-     * @param array    $fields
-     * @param array    $directives
-     * @param Location $location
+     * @param string $name
+     * @param string $alias
      */
     public function __construct($name, $alias, array $arguments, array $fields, array $directives, Location $location)
     {
         parent::__construct($location);
 
-        $this->name      = $name;
-        $this->alias     = $alias;
+        $this->name = $name;
+        $this->alias = $alias;
         $this->setFields($fields);
         $this->setArguments($arguments);
         $this->setDirectives($directives);
     }
 
-    public function getName()
+    public function getName(): string
     {
         return $this->name;
     }
@@ -55,15 +51,12 @@ public function getName()
     /**
      * @return Field[]|Query[]|FragmentInterface[]
      */
-    public function getFields()
+    public function getFields(): array
     {
         return array_values($this->fields);
     }
 
-    /**
-     * @return bool
-     */
-    public function hasFields()
+    public function hasFields(): bool
     {
         return (bool)count($this->fields);
     }
@@ -71,30 +64,28 @@ public function hasFields()
     /**
      * @param Field[]|Query[] $fields
      */
-    public function setFields($fields)
+    public function setFields($fields): void
     {
         /**
          * we cannot store fields by name because of TypedFragments
          */
         $this->fields = $fields;
-        }
+    }
 
-    public function getAlias()
+    public function getAlias(): ?string
     {
         return $this->alias;
     }
 
-    public function hasField($name, $deep = false)
+    public function hasField($name, $deep = false): bool
     {
         foreach ($this->getFields() as $field) {
             if ($field->getName() == $name) {
                 return true;
             }
 
-            if ($deep && $field instanceof Query) {
-                if ($field->hasField($name)) {
-                    return true;
-                }
+            if ($deep && $field instanceof Query && $field->hasField($name)) {
+                return true;
             }
         }
 
diff --git a/src/Parser/Ast/TypedFragmentReference.php b/src/Parser/Ast/TypedFragmentReference.php
index 749c6bbe..987dd99a 100644
--- a/src/Parser/Ast/TypedFragmentReference.php
+++ b/src/Parser/Ast/TypedFragmentReference.php
@@ -16,30 +16,29 @@ class TypedFragmentReference extends AbstractAst implements FragmentInterface
     use AstDirectivesTrait;
 
     /** @var Field[]|Query[] */
-    protected $fields;
+    protected array $fields;
 
     /** @var string */
     protected $typeName;
 
     /**
-     * @param string          $typeName
+     * @param string $typeName
      * @param Field[]|Query[] $fields
-     * @param Directive[]     $directives
-     * @param Location        $location
+     * @param Directive[] $directives
      */
     public function __construct($typeName, array $fields, array $directives, Location $location)
     {
         parent::__construct($location);
 
         $this->typeName = $typeName;
-        $this->fields   = $fields;
+        $this->fields = $fields;
         $this->setDirectives($directives);
     }
 
     /**
      * @return Field[]|Query[]
      */
-    public function getFields()
+    public function getFields(): array
     {
         return $this->fields;
     }
@@ -47,7 +46,7 @@ public function getFields()
     /**
      * @param Field[]|Query[] $fields
      */
-    public function setFields($fields)
+    public function setFields(array $fields): void
     {
         $this->fields = $fields;
     }
@@ -63,7 +62,7 @@ public function getTypeName()
     /**
      * @param string $typeName
      */
-    public function setTypeName($typeName)
+    public function setTypeName($typeName): void
     {
         $this->typeName = $typeName;
     }
diff --git a/src/Parser/Location.php b/src/Parser/Location.php
index adb5cf20..dd514e96 100644
--- a/src/Parser/Location.php
+++ b/src/Parser/Location.php
@@ -19,7 +19,7 @@ class Location
 
     public function __construct($line, $column)
     {
-        $this->line   = $line;
+        $this->line = $line;
         $this->column = $column;
     }
 
@@ -40,10 +40,10 @@ public function getColumn()
     }
 
 
-    public function toArray()
+    public function toArray(): array
     {
         return [
-            'line'   => $this->getLine(),
+            'line' => $this->getLine(),
             'column' => $this->getColumn()
         ];
     }
diff --git a/src/Parser/Parser.php b/src/Parser/Parser.php
index d3dad3cc..b289f9c4 100644
--- a/src/Parser/Parser.php
+++ b/src/Parser/Parser.php
@@ -27,10 +27,12 @@
 class Parser extends Tokenizer
 {
 
-    /** @var array */
-    private $data = [];
+    private array $data = [];
 
-    public function parse($source = null)
+    /**
+     * @throws SyntaxErrorException
+     */
+    public function parse($source = null): array
     {
         $this->init($source);
 
@@ -45,7 +47,7 @@ public function parse($source = null)
 
                     break;
                 case Token::TYPE_QUERY:
-                    $queries = $this->parseOperation(Token::TYPE_QUERY);
+                    $queries = $this->parseOperation();
                     foreach ($queries as $query) {
                         $this->data['queries'][] = $query;
                     }
@@ -72,23 +74,28 @@ public function parse($source = null)
         return $this->data;
     }
 
-    private function init($source = null)
+    private function init($source = null): void
     {
         $this->initTokenizer($source);
 
         $this->data = [
-            'queries'            => [],
-            'mutations'          => [],
-            'fragments'          => [],
+            'queries' => [],
+            'mutations' => [],
+            'fragments' => [],
             'fragmentReferences' => [],
-            'variables'          => [],
+            'variables' => [],
             'variableReferences' => [],
         ];
     }
 
-    protected function parseOperation($type = Token::TYPE_QUERY)
+    /**
+     * @return mixed[]
+     * @throws SyntaxErrorException
+     * @throws SyntaxErrorException
+     */
+    protected function parseOperation($type = Token::TYPE_QUERY): array
     {
-        $operation  = null;
+        $operation = null;
         $directives = [];
 
         if ($this->matchMulti([Token::TYPE_QUERY, Token::TYPE_MUTATION])) {
@@ -113,7 +120,7 @@ protected function parseOperation($type = Token::TYPE_QUERY)
         while (!$this->match(Token::TYPE_RBRACE) && !$this->end()) {
             $this->eatMulti([Token::TYPE_COMMA]);
 
-            $operation = $this->parseBodyItem($type, true);
+            $operation = $this->parseBodyItem($type);
             $operation->setDirectives($directives);
 
             $fields[] = $operation;
@@ -124,7 +131,13 @@ protected function parseOperation($type = Token::TYPE_QUERY)
         return $fields;
     }
 
-    protected function parseBody($token = Token::TYPE_QUERY, $highLevel = true)
+    /**
+     * @return mixed[]
+     * @throws SyntaxErrorException
+     * @throws SyntaxErrorException
+     * @throws SyntaxErrorException
+     */
+    protected function parseBody($token = Token::TYPE_QUERY, $highLevel = true): array
     {
         $fields = [];
 
@@ -151,6 +164,9 @@ protected function parseBody($token = Token::TYPE_QUERY, $highLevel = true)
         return $fields;
     }
 
+    /**
+     * @throws SyntaxErrorException
+     */
     protected function parseVariables()
     {
         $this->eat(Token::TYPE_LPAREN);
@@ -159,10 +175,10 @@ protected function parseVariables()
             $this->eat(Token::TYPE_COMMA);
 
             $variableToken = $this->eat(Token::TYPE_VARIABLE);
-            $nameToken     = $this->eatIdentifierToken();
+            $nameToken = $this->eatIdentifierToken();
             $this->eat(Token::TYPE_COLON);
 
-            $isArray              = false;
+            $isArray = false;
             $arrayElementNullable = true;
 
             if ($this->match(Token::TYPE_LSQUARE_BRACE)) {
@@ -192,8 +208,8 @@ protected function parseVariables()
                 $type,
                 $required,
                 $isArray,
-                $arrayElementNullable,
-                new Location($variableToken->getLine(), $variableToken->getColumn())
+                new Location($variableToken->getLine(), $variableToken->getColumn()),
+                $arrayElementNullable
             );
 
             if ($this->match(Token::TYPE_EQUAL)) {
@@ -207,6 +223,9 @@ protected function parseVariables()
         $this->expect(Token::TYPE_RPAREN);
     }
 
+    /**
+     * @throws SyntaxErrorException
+     */
     protected function expectMulti($types)
     {
         if ($this->matchMulti($types)) {
@@ -216,6 +235,9 @@ protected function expectMulti($types)
         throw $this->createUnexpectedException($this->peek());
     }
 
+    /**
+     * @throws SyntaxErrorException
+     */
     protected function parseVariableReference()
     {
         $startToken = $this->expectMulti([Token::TYPE_VARIABLE]);
@@ -224,11 +246,9 @@ protected function parseVariableReference()
             $name = $this->lex()->getData();
 
             $variable = $this->findVariable($name);
-            if ($variable) {
-                $variable->setUsed(true);
-            }
+            $variable?->setUsed(true);
 
-            $variableReference = new VariableReference($name, $variable, new Location($startToken->getLine(), $startToken->getColumn()));
+            $variableReference = new VariableReference($name, new Location($startToken->getLine(), $startToken->getColumn()), $variable);
 
             $this->data['variableReferences'][] = $variableReference;
 
@@ -240,7 +260,7 @@ protected function parseVariableReference()
 
     protected function findVariable($name)
     {
-        foreach ((array) $this->data['variables'] as $variable) {
+        foreach ((array)$this->data['variables'] as $variable) {
             /** @var $variable Variable */
             if ($variable->getName() === $name) {
                 return $variable;
@@ -250,9 +270,9 @@ protected function findVariable($name)
         return null;
     }
 
-    protected function parseFragmentReference()
+    protected function parseFragmentReference(): FragmentReference
     {
-        $nameToken         = $this->eatIdentifierToken();
+        $nameToken = $this->eatIdentifierToken();
         $fragmentReference = new FragmentReference($nameToken->getData(), new Location($nameToken->getLine(), $nameToken->getColumn()));
 
         $this->data['fragmentReferences'][] = $fragmentReference;
@@ -260,6 +280,9 @@ protected function parseFragmentReference()
         return $fragmentReference;
     }
 
+    /**
+     * @throws SyntaxErrorException
+     */
     protected function eatIdentifierToken()
     {
         return $this->expectMulti([
@@ -270,24 +293,27 @@ protected function eatIdentifierToken()
         ]);
     }
 
-    protected function parseBodyItem($type = Token::TYPE_QUERY, $highLevel = true)
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function parseBodyItem($type = Token::TYPE_QUERY, $highLevel = true): Query|TypedFragmentReference|Mutation|Field
     {
         $nameToken = $this->eatIdentifierToken();
-        $alias     = null;
+        $alias = null;
 
         if ($this->eat(Token::TYPE_COLON)) {
-            $alias     = $nameToken->getData();
+            $alias = $nameToken->getData();
             $nameToken = $this->eatIdentifierToken();
         }
 
         $bodyLocation = new Location($nameToken->getLine(), $nameToken->getColumn());
-        $arguments    = $this->match(Token::TYPE_LPAREN) ? $this->parseArgumentList() : [];
-        $directives   = $this->match(Token::TYPE_AT) ? $this->parseDirectiveList() : [];
+        $arguments = $this->match(Token::TYPE_LPAREN) ? $this->parseArgumentList() : [];
+        $directives = $this->match(Token::TYPE_AT) ? $this->parseDirectiveList() : [];
 
         if ($this->match(Token::TYPE_LBRACE)) {
             $fields = $this->parseBody($type === Token::TYPE_TYPED_FRAGMENT ? Token::TYPE_QUERY : $type, false);
 
-            if (!$fields) {
+            if ($fields === []) {
                 throw $this->createUnexpectedTokenTypeException($this->lookAhead->getType());
             }
 
@@ -309,7 +335,12 @@ protected function parseBodyItem($type = Token::TYPE_QUERY, $highLevel = true)
         }
     }
 
-    protected function parseArgumentList()
+    /**
+     * @return mixed[]
+     * @throws SyntaxErrorException
+     * @throws SyntaxErrorException
+     */
+    protected function parseArgumentList(): array
     {
         $args = [];
 
@@ -325,7 +356,10 @@ protected function parseArgumentList()
         return $args;
     }
 
-    protected function parseArgument()
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function parseArgument(): Argument
     {
         $nameToken = $this->eatIdentifierToken();
         $this->expect(Token::TYPE_COLON);
@@ -334,7 +368,10 @@ protected function parseArgument()
         return new Argument($nameToken->getData(), $value, new Location($nameToken->getLine(), $nameToken->getColumn()));
     }
 
-    protected function parseDirectiveList()
+    /**
+     * @return mixed[]
+     */
+    protected function parseDirectiveList(): array
     {
         $directives = [];
 
@@ -346,12 +383,15 @@ protected function parseDirectiveList()
         return $directives;
     }
 
-    protected function parseDirective()
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function parseDirective(): Directive
     {
         $this->expect(Token::TYPE_AT);
 
         $nameToken = $this->eatIdentifierToken();
-        $args      = $this->match(Token::TYPE_LPAREN) ? $this->parseArgumentList() : [];
+        $args = $this->match(Token::TYPE_LPAREN) ? $this->parseArgumentList() : [];
 
         return new Directive($nameToken->getData(), $args, new Location($nameToken->getLine(), $nameToken->getColumn()));
     }
@@ -387,7 +427,10 @@ protected function parseValue()
         throw $this->createUnexpectedException($this->lookAhead);
     }
 
-    protected function parseList($createType = true)
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function parseList($createType = true): InputList|array
     {
         $startToken = $this->eat(Token::TYPE_LSQUARE_BRACE);
 
@@ -403,6 +446,9 @@ protected function parseList($createType = true)
         return $createType ? new InputList($list, new Location($startToken->getLine(), $startToken->getColumn())) : $list;
     }
 
+    /**
+     * @throws SyntaxErrorException
+     */
     protected function parseListValue()
     {
         switch ($this->lookAhead->getType()) {
@@ -418,16 +464,19 @@ protected function parseListValue()
                 return $this->parseVariableReference();
 
             case Token::TYPE_LBRACE:
-                return $this->parseObject(true);
+                return $this->parseObject();
 
             case Token::TYPE_LSQUARE_BRACE:
                 return $this->parseList(false);
         }
 
-        throw new SyntaxErrorException('Can\'t parse argument', $this->getLocation());
+        throw new SyntaxErrorException("Can't parse argument", $this->getLocation());
     }
 
-    protected function parseObject($createType = true)
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function parseObject($createType = true): InputObject|array
     {
         $startToken = $this->eat(Token::TYPE_LBRACE);
 
@@ -447,7 +496,7 @@ protected function parseObject($createType = true)
         return $createType ? new InputObject($object, new Location($startToken->getLine(), $startToken->getColumn())) : $object;
     }
 
-    protected function parseFragment()
+    protected function parseFragment(): Fragment
     {
         $this->lex();
         $nameToken = $this->eatIdentifierToken();
@@ -481,14 +530,8 @@ protected function eatMulti($types)
         return null;
     }
 
-    protected function matchMulti($types)
+    protected function matchMulti($types): bool
     {
-        foreach ((array) $types as $type) {
-            if ($this->peek()->getType() === $type) {
-                return true;
-            }
-        }
-
-        return false;
+        return in_array($this->peek()->getType(), (array)$types, true);
     }
 }
diff --git a/src/Parser/Token.php b/src/Parser/Token.php
index 92eebdaa..bf5aaa45 100644
--- a/src/Parser/Token.php
+++ b/src/Parser/Token.php
@@ -10,35 +10,57 @@
 class Token
 {
 
-    const TYPE_END        = 'end';
-    const TYPE_IDENTIFIER = 'identifier';
-    const TYPE_NUMBER     = 'number';
-    const TYPE_STRING     = 'string';
-    const TYPE_ON         = 'on';
-
-    const TYPE_QUERY              = 'query';
-    const TYPE_MUTATION           = 'mutation';
-    const TYPE_FRAGMENT           = 'fragment';
-    const TYPE_FRAGMENT_REFERENCE = '...';
-    const TYPE_TYPED_FRAGMENT     = 'typed fragment';
-
-    const TYPE_LBRACE        = '{';
-    const TYPE_RBRACE        = '}';
-    const TYPE_LPAREN        = '(';
-    const TYPE_RPAREN        = ')';
-    const TYPE_LSQUARE_BRACE = '[';
-    const TYPE_RSQUARE_BRACE = ']';
-    const TYPE_COLON         = ':';
-    const TYPE_COMMA         = ',';
-    const TYPE_VARIABLE      = '$';
-    const TYPE_POINT         = '.';
-    const TYPE_REQUIRED      = '!';
-    const TYPE_EQUAL         = '=';
-    const TYPE_AT            = '@';
-
-    const TYPE_NULL  = 'null';
-    const TYPE_TRUE  = 'true';
-    const TYPE_FALSE = 'false';
+    final const TYPE_END = 'end';
+
+    final const TYPE_IDENTIFIER = 'identifier';
+
+    final const TYPE_NUMBER = 'number';
+
+    final const TYPE_STRING = 'string';
+
+    final const TYPE_ON = 'on';
+
+    final const TYPE_QUERY = 'query';
+
+    final const TYPE_MUTATION = 'mutation';
+
+    final const TYPE_FRAGMENT = 'fragment';
+
+    final const TYPE_FRAGMENT_REFERENCE = '...';
+
+    final const TYPE_TYPED_FRAGMENT = 'typed fragment';
+
+    final const TYPE_LBRACE = '{';
+
+    final const TYPE_RBRACE = '}';
+
+    final const TYPE_LPAREN = '(';
+
+    final const TYPE_RPAREN = ')';
+
+    final const TYPE_LSQUARE_BRACE = '[';
+
+    final const TYPE_RSQUARE_BRACE = ']';
+
+    final const TYPE_COLON = ':';
+
+    final const TYPE_COMMA = ',';
+
+    final const TYPE_VARIABLE = '$';
+
+    final const TYPE_POINT = '.';
+
+    final const TYPE_REQUIRED = '!';
+
+    final const TYPE_EQUAL = '=';
+
+    final const TYPE_AT = '@';
+
+    final const TYPE_NULL = 'null';
+
+    final const TYPE_TRUE = 'true';
+
+    final const TYPE_FALSE = 'false';
 
 
     /** @var mixed */
@@ -58,11 +80,11 @@ public function __construct($type, $line, $column, $data = null)
         $this->type = $type;
         $this->data = $data;
 
-        $this->line   = $line;
+        $this->line = $line;
         $this->column = $column;
 
         if ($data) {
-            $tokenLength = mb_strlen($data);
+            $tokenLength = mb_strlen((string)$data);
             $tokenLength = $tokenLength > 1 ? $tokenLength - 1 : 0;
 
             $this->column = $column - $tokenLength;
@@ -81,34 +103,34 @@ public function __construct($type, $line, $column, $data = null)
         }
     }
 
-    public static function tokenName($tokenType)
+    public static function tokenName(string $tokenType): string
     {
         return [
-            self::TYPE_END                => 'END',
-            self::TYPE_IDENTIFIER         => 'IDENTIFIER',
-            self::TYPE_NUMBER             => 'NUMBER',
-            self::TYPE_STRING             => 'STRING',
-            self::TYPE_ON                 => 'ON',
-            self::TYPE_QUERY              => 'QUERY',
-            self::TYPE_MUTATION           => 'MUTATION',
-            self::TYPE_FRAGMENT           => 'FRAGMENT',
+            self::TYPE_END => 'END',
+            self::TYPE_IDENTIFIER => 'IDENTIFIER',
+            self::TYPE_NUMBER => 'NUMBER',
+            self::TYPE_STRING => 'STRING',
+            self::TYPE_ON => 'ON',
+            self::TYPE_QUERY => 'QUERY',
+            self::TYPE_MUTATION => 'MUTATION',
+            self::TYPE_FRAGMENT => 'FRAGMENT',
             self::TYPE_FRAGMENT_REFERENCE => 'FRAGMENT_REFERENCE',
-            self::TYPE_TYPED_FRAGMENT     => 'TYPED_FRAGMENT',
-            self::TYPE_LBRACE             => 'LBRACE',
-            self::TYPE_RBRACE             => 'RBRACE',
-            self::TYPE_LPAREN             => 'LPAREN',
-            self::TYPE_RPAREN             => 'RPAREN',
-            self::TYPE_LSQUARE_BRACE      => 'LSQUARE_BRACE',
-            self::TYPE_RSQUARE_BRACE      => 'RSQUARE_BRACE',
-            self::TYPE_COLON              => 'COLON',
-            self::TYPE_COMMA              => 'COMMA',
-            self::TYPE_VARIABLE           => 'VARIABLE',
-            self::TYPE_POINT              => 'POINT',
-            self::TYPE_NULL               => 'NULL',
-            self::TYPE_TRUE               => 'TRUE',
-            self::TYPE_FALSE              => 'FALSE',
-            self::TYPE_REQUIRED           => 'REQUIRED',
-            self::TYPE_AT                 => 'AT',
+            self::TYPE_TYPED_FRAGMENT => 'TYPED_FRAGMENT',
+            self::TYPE_LBRACE => 'LBRACE',
+            self::TYPE_RBRACE => 'RBRACE',
+            self::TYPE_LPAREN => 'LPAREN',
+            self::TYPE_RPAREN => 'RPAREN',
+            self::TYPE_LSQUARE_BRACE => 'LSQUARE_BRACE',
+            self::TYPE_RSQUARE_BRACE => 'RSQUARE_BRACE',
+            self::TYPE_COLON => 'COLON',
+            self::TYPE_COMMA => 'COMMA',
+            self::TYPE_VARIABLE => 'VARIABLE',
+            self::TYPE_POINT => 'POINT',
+            self::TYPE_NULL => 'NULL',
+            self::TYPE_TRUE => 'TRUE',
+            self::TYPE_FALSE => 'FALSE',
+            self::TYPE_REQUIRED => 'REQUIRED',
+            self::TYPE_AT => 'AT',
         ][$tokenType];
     }
 
diff --git a/src/Parser/Tokenizer.php b/src/Parser/Tokenizer.php
index 7d3c57a7..c63af8e1 100644
--- a/src/Parser/Tokenizer.php
+++ b/src/Parser/Tokenizer.php
@@ -12,54 +12,59 @@
 class Tokenizer
 {
     protected $source;
-    protected $pos = 0;
-    protected $line = 1;
-    protected $lineStart = 0;
+
+    protected int $pos = 0;
+
+    protected int $line = 1;
+
+    protected int $lineStart = 0;
 
     /** @var  Token */
-    protected $lookAhead;
+    protected Token $lookAhead;
 
-    protected function initTokenizer($source)
+    protected function initTokenizer($source): void
     {
-        $this->source    = $source;
+        $this->source = $source;
         $this->lookAhead = $this->next();
     }
 
     /**
      * @return Token
+     * @throws SyntaxErrorException
      */
-    protected function next()
+    protected function next(): Token
     {
         $this->skipWhitespace();
 
         return $this->scan();
     }
 
-    protected function skipWhitespace()
+    protected function skipWhitespace(): void
     {
-        while ($this->pos < strlen($this->source)) {
+        while ($this->pos < strlen((string)$this->source)) {
             $ch = $this->source[$this->pos];
-            if ($ch === ' ' || $ch === "\t" || $ch === ',') {
-                $this->pos++;
+            if (in_array($ch, [' ', "\t", ','], true)) {
+                ++$this->pos;
             } elseif ($ch === '#') {
-                $this->pos++;
+                ++$this->pos;
                 while (
-                    $this->pos < strlen($this->source) &&
+                    $this->pos < strlen((string)$this->source) &&
                     ($code = ord($this->source[$this->pos])) &&
                     $code !== 10 && $code !== 13 && $code !== 0x2028 && $code !== 0x2029
                 ) {
-                    $this->pos++;
+                    ++$this->pos;
                 }
             } elseif ($ch === "\r") {
-                $this->pos++;
+                ++$this->pos;
                 if ($this->source[$this->pos] === "\n") {
-                    $this->pos++;
+                    ++$this->pos;
                 }
-                $this->line++;
+
+                ++$this->line;
                 $this->lineStart = $this->pos;
             } elseif ($ch === "\n") {
-                $this->pos++;
-                $this->line++;
+                ++$this->pos;
+                ++$this->line;
                 $this->lineStart = $this->pos;
             } else {
                 break;
@@ -72,9 +77,9 @@ protected function skipWhitespace()
      *
      * @throws SyntaxErrorException
      */
-    protected function scan()
+    protected function scan(): Token
     {
-        if ($this->pos >= strlen($this->source)) {
+        if ($this->pos >= strlen((string)$this->source)) {
             return new Token(Token::TYPE_END, $this->getLine(), $this->getColumn());
         }
 
@@ -155,18 +160,18 @@ protected function scan()
         throw $this->createException('Can\t recognize token type');
     }
 
-    protected function checkFragment()
+    protected function checkFragment(): bool
     {
-        $this->pos++;
+        ++$this->pos;
         $ch = $this->source[$this->pos];
 
-        $this->pos++;
+        ++$this->pos;
         $nextCh = $this->source[$this->pos];
 
         $isset = $ch == Token::TYPE_POINT && $nextCh == Token::TYPE_POINT;
 
         if ($isset) {
-            $this->pos++;
+            ++$this->pos;
 
             return true;
         }
@@ -174,55 +179,45 @@ protected function checkFragment()
         return false;
     }
 
-    protected function scanWord()
+    protected function scanWord(): Token
     {
         $start = $this->pos;
-        $this->pos++;
+        ++$this->pos;
 
-        while ($this->pos < strlen($this->source)) {
+        while ($this->pos < strlen((string)$this->source)) {
             $ch = $this->source[$this->pos];
 
             if ($ch === '_' || $ch === '$' || ('a' <= $ch && $ch <= 'z') || ('A' <= $ch && $ch <= 'Z') || ('0' <= $ch && $ch <= '9')) {
-                $this->pos++;
+                ++$this->pos;
             } else {
                 break;
             }
         }
 
-        $value = substr($this->source, $start, $this->pos - $start);
+        $value = substr((string)$this->source, $start, $this->pos - $start);
 
         return new Token($this->getKeyword($value), $this->getLine(), $this->getColumn(), $value);
     }
 
-    protected function getKeyword($name)
+    protected function getKeyword($name): string
     {
-        switch ($name) {
-            case 'null':
-                return Token::TYPE_NULL;
-
-            case 'true':
-                return Token::TYPE_TRUE;
-
-            case 'false':
-                return Token::TYPE_FALSE;
-
-            case 'query':
-                return Token::TYPE_QUERY;
-
-            case 'fragment':
-                return Token::TYPE_FRAGMENT;
+        return match ($name) {
+            'null' => Token::TYPE_NULL,
+            'true' => Token::TYPE_TRUE,
+            'false' => Token::TYPE_FALSE,
+            'query' => Token::TYPE_QUERY,
+            'fragment' => Token::TYPE_FRAGMENT,
+            'mutation' => Token::TYPE_MUTATION,
+            'on' => Token::TYPE_ON,
+            default => Token::TYPE_IDENTIFIER,
+        };
 
-            case 'mutation':
-                return Token::TYPE_MUTATION;
-
-            case 'on':
-                return Token::TYPE_ON;
-        }
-
-        return Token::TYPE_IDENTIFIER;
     }
 
-    protected function expect($type)
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function expect($type): Token
     {
         if ($this->match($type)) {
             return $this->lex();
@@ -231,12 +226,12 @@ protected function expect($type)
         throw $this->createUnexpectedException($this->peek());
     }
 
-    protected function match($type)
+    protected function match($type): bool
     {
         return $this->peek()->getType() === $type;
     }
 
-    protected function scanNumber()
+    protected function scanNumber(): Token
     {
         $start = $this->pos;
         if ($this->source[$this->pos] === '-') {
@@ -246,49 +241,45 @@ protected function scanNumber()
         $this->skipInteger();
 
         if (isset($this->source[$this->pos]) && $this->source[$this->pos] === '.') {
-            $this->pos++;
+            ++$this->pos;
             $this->skipInteger();
         }
 
-        $value = substr($this->source, $start, $this->pos - $start);
+        $value = substr((string)$this->source, $start, $this->pos - $start);
 
-        if (strpos($value, '.') === false) {
-            $value = (int) $value;
-        } else {
-            $value = (float) $value;
-        }
+        $value = str_contains($value, '.') ? (float)$value : (int)$value;
 
         return new Token(Token::TYPE_NUMBER, $this->getLine(), $this->getColumn(), $value);
     }
 
-    protected function skipInteger()
+    protected function skipInteger(): void
     {
-        while ($this->pos < strlen($this->source)) {
+        while ($this->pos < strlen((string)$this->source)) {
             $ch = $this->source[$this->pos];
             if ('0' <= $ch && $ch <= '9') {
-                $this->pos++;
+                ++$this->pos;
             } else {
                 break;
             }
         }
     }
 
-    protected function createException($message)
+    protected function createException(string $message): SyntaxErrorException
     {
-        return new SyntaxErrorException(sprintf('%s', $message), $this->getLocation());
+        return new SyntaxErrorException($message, $this->getLocation());
     }
 
-    protected function getLocation()
+    protected function getLocation(): Location
     {
         return new Location($this->getLine(), $this->getColumn());
     }
 
-    protected function getColumn()
+    protected function getColumn(): int|float
     {
         return $this->pos - $this->lineStart;
     }
 
-    protected function getLine()
+    protected function getLine(): int
     {
         return $this->line;
     }
@@ -296,25 +287,28 @@ protected function getLine()
     /*
   		http://facebook.github.io/graphql/October2016/#sec-String-Value
     */
-    protected function scanString()
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function scanString(): Token
     {
-        $len = strlen($this->source);
-        $this->pos++;
+        $len = strlen((string)$this->source);
+        ++$this->pos;
 
         $value = '';
         while ($this->pos < $len) {
             $ch = $this->source[$this->pos];
             if ($ch === '"') {
                 $token = new Token(Token::TYPE_STRING, $this->getLine(), $this->getColumn(), $value);
-                $this->pos++;
+                ++$this->pos;
 
                 return $token;
             }
-            
-            if($ch === '\\' && ($this->pos < ($len - 1))) {
-                $this->pos++;
+
+            if ($ch === '\\' && ($this->pos < ($len - 1))) {
+                ++$this->pos;
                 $ch = $this->source[$this->pos];
-                switch($ch) {
+                switch ($ch) {
                     case '"':
                     case '\\':
                     case '/':
@@ -332,51 +326,54 @@ protected function scanString()
                         $ch = "\r";
                         break;
                     case 'u':
-                        $codepoint = substr($this->source, $this->pos + 1, 4);
-                        if( !preg_match('/[0-9A-Fa-f]{4}/', $codepoint)) {
+                        $codepoint = substr((string)$this->source, $this->pos + 1, 4);
+                        if (!preg_match('/[0-9A-Fa-f]{4}/', $codepoint)) {
                             throw $this->createException(sprintf('Invalid string unicode escape sequece "%s"', $codepoint));
                         }
-                        $ch = html_entity_decode("&#x{$codepoint};", ENT_QUOTES, 'UTF-8');
+
+                        $ch = html_entity_decode(sprintf('&#x%s;', $codepoint), ENT_QUOTES, 'UTF-8');
                         $this->pos += 4;
                         break;
                     default:
                         throw $this->createException(sprintf('Unexpected string escaped character "%s"', $ch));
-                        break;
 
                 }
-            } 
-            
+            }
+
             $value .= $ch;
-            $this->pos++;
+            ++$this->pos;
         }
 
         throw $this->createUnexpectedTokenTypeException(Token::TYPE_END);
     }
 
-    protected function end()
+    protected function end(): bool
     {
         return $this->lookAhead->getType() === Token::TYPE_END;
     }
 
-    protected function peek()
+    protected function peek(): Token
     {
         return $this->lookAhead;
     }
 
-    protected function lex()
+    /**
+     * @throws SyntaxErrorException
+     */
+    protected function lex(): Token
     {
-        $prev            = $this->lookAhead;
+        $prev = $this->lookAhead;
         $this->lookAhead = $this->next();
 
         return $prev;
     }
 
-    protected function createUnexpectedException(Token $token)
+    protected function createUnexpectedException(Token $token): SyntaxErrorException
     {
         return $this->createUnexpectedTokenTypeException($token->getType());
     }
 
-    protected function createUnexpectedTokenTypeException($tokenType)
+    protected function createUnexpectedTokenTypeException(string $tokenType): SyntaxErrorException
     {
         return $this->createException(sprintf('Unexpected token "%s"', Token::tokenName($tokenType)));
     }
diff --git a/src/Relay/Connection/ArrayConnection.php b/src/Relay/Connection/ArrayConnection.php
index e1b1750c..bd66c554 100644
--- a/src/Relay/Connection/ArrayConnection.php
+++ b/src/Relay/Connection/ArrayConnection.php
@@ -7,18 +7,18 @@
 
 namespace Youshido\GraphQL\Relay\Connection;
 
-
 class ArrayConnection
 {
+    final const PREFIX = 'arrayconnection:';
 
-    const PREFIX = 'arrayconnection:';
-
-    public static function cursorForObjectInConnection($data, $object)
+    public static function cursorForObjectInConnection($data, $object): ?string
     {
-        if (!is_array($data)) return null;
+        if (!is_array($data)) {
+            return null;
+        }
 
-        $index = array_search($object, $data);
-        return $index === false ? null : (string) self::keyToCursor($index);
+        $index = array_search($object, $data, true);
+        return $index === false ? null : self::keyToCursor($index);
     }
 
     /**
@@ -27,87 +27,86 @@ public static function cursorForObjectInConnection($data, $object)
      * @deprecated
      *   Use keyToCursor instead.
      */
-    public static function offsetToCursor($offset)
+    public static function offsetToCursor(int $offset): string
     {
-      return self::keyToCursor($offset);
+        return self::keyToCursor($offset);
     }
 
-    public static function keyToCursor($key)
+    public static function keyToCursor(string $key): string
     {
-      return base64_encode(self::PREFIX . $key);
+        return base64_encode(self::PREFIX . $key);
     }
 
     /**
      * @param $cursor string
      *
-     * @return int|null
+     * @return int|string|null
      * @deprecated Use cursorToKey instead.
      */
-    public static function cursorToOffset($cursor)
+    public static function cursorToOffset(string $cursor): int|string|null
     {
         return self::cursorToKey($cursor);
     }
 
-  /**
-   * Converts a cursor to its array key.
-   *
-   * @param $cursor
-   * @return null|string
-   */
-    public static function cursorToKey($cursor) {
-      if ($decoded = base64_decode($cursor)) {
-        return substr($decoded, strlen(self::PREFIX));
-      }
-      return null;
+    /**
+     * Converts a cursor to its array key.
+     */
+    public static function cursorToKey(?string $cursor): ?string
+    {
+        if ($cursor === null) {
+            return null;
+        }
+
+        $decoded = base64_decode($cursor);
+
+        if ($decoded !== '' && $decoded !== '0') {
+            return substr($decoded, strlen(self::PREFIX));
+        }
+
+        return null;
     }
 
-  /**
-   * Converts a cursor to an array offset.
-   *
-   * @param $cursor
-   *   The cursor string.
-   * @param $default
-   *   The default value, in case the cursor is not given.
-   * @param array $array
-   *   The array to use in counting the offset. If empty, assumed to be an indexed array.
-   * @return int|null
-   */
-    public static function cursorToOffsetWithDefault($cursor, $default, $array = [])
+    /**
+     * Converts a cursor to an array offset.
+     *
+     * @param $cursor
+     *   The cursor string.
+     * @param $default
+     *   The default value, in case the cursor is not given.
+     * @param array $array
+     *   The array to use in counting the offset. If empty, assumed to be an indexed array.
+     */
+    public static function cursorToOffsetWithDefault(mixed $cursor, mixed $default, array $array = []): ?int
     {
         if (!is_string($cursor)) {
             return $default;
         }
 
         $key = self::cursorToKey($cursor);
-        if (empty($array)) {
-          $offset = $key;
-        }
-        else {
-          $offset = array_search($key, array_keys($array));
-        }
+        $offset = $array === [] ? $key : array_search($key, array_keys($array), true);
 
-        return is_null($offset) ? $default : (int) $offset;
+        return is_null($offset) ? $default : (int)$offset;
     }
 
-    public static function connectionFromArray(array $data, array $args = [])
+    public static function connectionFromArray(array $data, array $args = []): array
     {
         return self::connectionFromArraySlice($data, $args, 0, count($data));
     }
 
-    public static function connectionFromArraySlice(array $data, array $args, $sliceStart, $arrayLength)
+    public static function connectionFromArraySlice(array $data, array $args, $sliceStart, $arrayLength): array
     {
-        $after  = isset($args['after']) ? $args['after'] : null;
-        $before = isset($args['before']) ? $args['before'] : null;
-        $first  = isset($args['first']) ? $args['first'] : null;
-        $last   = isset($args['last']) ? $args['last'] : null;
+        $after = $args['after'] ?? null;
+        $before = $args['before'] ?? null;
+        $first = $args['first'] ?? null;
+        $last = $args['last'] ?? null;
 
         $sliceEnd = $sliceStart + count($data);
 
         $beforeOffset = ArrayConnection::cursorToOffsetWithDefault($before, $arrayLength, $data);
-        $afterOffset  = ArrayConnection::cursorToOffsetWithDefault($after, -1, $data);
+        $afterOffset = ArrayConnection::cursorToOffsetWithDefault($after, -1, $data);
 
         $startOffset = max($sliceStart - 1, $afterOffset, -1) + 1;
-        $endOffset   = min($sliceEnd, $beforeOffset, $arrayLength);
+        $endOffset = min($sliceEnd, $beforeOffset, $arrayLength);
 
         if ($first) {
             $endOffset = min($endOffset, $startOffset + $first);
@@ -117,34 +116,34 @@ public static function connectionFromArraySlice(array $data, array $args, $slice
             $startOffset = max($startOffset, $endOffset - $last);
         }
 
-        $arraySliceStart    = max($startOffset - $sliceStart, 0);
-        $arraySliceEnd      = count($data) - ($sliceEnd - $endOffset) - $arraySliceStart;
+        $arraySliceStart = max($startOffset - $sliceStart, 0);
+        $arraySliceEnd = count($data) - ($sliceEnd - $endOffset) - $arraySliceStart;
 
         $slice = array_slice($data, $arraySliceStart, $arraySliceEnd, true);
         $edges = array_map(['self', 'edgeForObjectWithIndex'], $slice, array_keys($slice));
 
-        $firstEdge  = array_key_exists(0, $edges) ? $edges[0] : null;
-        $lastEdge   = count($edges) > 0 ? $edges[count($edges) - 1] : null;
+        $firstEdge = $edges[0] ?? null;
+        $lastEdge = $edges !== [] ? $edges[count($edges) - 1] : null;
         $lowerBound = $after ? $afterOffset + 1 : 0;
         $upperBound = $before ? $beforeOffset : $arrayLength;
 
         return [
             'totalCount' => $arrayLength,
-            'edges'      => $edges,
-            'pageInfo'   => [
-                'startCursor'     => $firstEdge ? $firstEdge['cursor'] : null,
-                'endCursor'       => $lastEdge ? $lastEdge['cursor'] : null,
-                'hasPreviousPage' => $last ? $startOffset > $lowerBound : false,
-                'hasNextPage'     => $first ? $endOffset < $upperBound : false,
+            'edges' => $edges,
+            'pageInfo' => [
+                'startCursor' => $firstEdge ? $firstEdge['cursor'] : null,
+                'endCursor' => $lastEdge ? $lastEdge['cursor'] : null,
+                'hasPreviousPage' => $last && $startOffset > $lowerBound,
+                'hasNextPage' => $first && $endOffset < $upperBound,
             ],
         ];
     }
 
-    public static function edgeForObjectWithIndex($object, $index)
+    public static function edgeForObjectWithIndex($object, string $index): array
     {
         return [
             'cursor' => ArrayConnection::keyToCursor($index),
-            'node'   => $object
+            'node' => $object
         ];
     }
 
diff --git a/src/Relay/Connection/Connection.php b/src/Relay/Connection/Connection.php
index 67ec001a..9b2b8e8d 100644
--- a/src/Relay/Connection/Connection.php
+++ b/src/Relay/Connection/Connection.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Relay\Connection;
 
 
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Relay\Type\PageInfoType;
 use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\ListType\ListType;
@@ -19,12 +20,12 @@
 class Connection
 {
 
-    public static function connectionArgs()
+    public static function connectionArgs(): array
     {
         return array_merge(self::forwardArgs(), self::backwardArgs());
     }
 
-    public static function forwardArgs()
+    public static function forwardArgs(): array
     {
         return [
             'after' => ['type' => TypeMap::TYPE_STRING],
@@ -32,101 +33,96 @@ public static function forwardArgs()
         ];
     }
 
-    public static function backwardArgs()
+    public static function backwardArgs(): array
     {
         return [
             'before' => ['type' => TypeMap::TYPE_STRING],
-            'last'   => ['type' => TypeMap::TYPE_INT]
+            'last' => ['type' => TypeMap::TYPE_INT]
         ];
     }
 
     /**
-     * @param AbstractType $type
-     * @param null|string  $name
-     * @param array        $config
+     * @param null|string $name
      * @option string  edgeFields
      *
-     * @return ObjectType
+     * @throws ConfigurationException
      */
-    public static function edgeDefinition(AbstractType $type, $name = null, $config = [])
+    public static function edgeDefinition(AbstractType $type, $name = null, array $config = []): ObjectType
     {
-        $name       = $name ?: $type->getName();
-        $edgeFields = !empty($config['edgeFields']) ? $config['edgeFields'] : [];
+        $name = $name ?: $type->getName();
+        $edgeFields = empty($config['edgeFields']) ? [] : $config['edgeFields'];
 
-        $edgeType = new ObjectType([
-            'name'        => $name . 'Edge',
+        return new ObjectType([
+            'name' => $name . 'Edge',
             'description' => 'An edge in a connection.',
-            'fields'      => array_merge([
-                'node'   => [
-                    'type'        => $type,
+            'fields' => array_merge([
+                'node' => [
+                    'type' => $type,
                     'description' => 'The item at the end of the edge',
-                    'resolve'     => [__CLASS__, 'getNode'],
+                    'resolve' => [__CLASS__, 'getNode'],
                 ],
                 'cursor' => [
-                    'type'        => TypeMap::TYPE_STRING,
+                    'type' => TypeMap::TYPE_STRING,
                     'description' => 'A cursor for use in pagination'
                 ]
             ], $edgeFields)
         ]);
-
-        return $edgeType;
     }
 
     /**
-     * @param AbstractType $type
-     * @param null|string  $name
-     * @param array        $config
+     * @param null|string $name
      * @option string  connectionFields
      *
-     * @return ObjectType
+     * @throws ConfigurationException
+     * @throws ConfigurationException
+     * @throws ConfigurationException
+     * @throws ConfigurationException
      */
-    public static function connectionDefinition(AbstractType $type, $name = null, $config = [])
+    public static function connectionDefinition(AbstractType $type, $name = null, array $config = []): ObjectType
     {
-        $name             = $name ?: $type->getName();
-        $connectionFields = !empty($config['connectionFields']) ? $config['connectionFields'] : [];
+        $name = $name ?: $type->getName();
+        $connectionFields = empty($config['connectionFields']) ? [] : $config['connectionFields'];
 
-        $connectionType = new ObjectType([
-            'name'        => $name . 'Connection',
+        return new ObjectType([
+            'name' => $name . 'Connection',
             'description' => 'A connection to a list of items.',
-            'fields'      => array_merge([
+            'fields' => array_merge([
                 'totalCount' => [
-                    'type'        => new NonNullType(new IntType()),
+                    'type' => new NonNullType(new IntType()),
                     'description' => 'How many nodes.',
-                    'resolve'     => [__CLASS__, 'getTotalCount'],
+                    'resolve' => [__CLASS__, 'getTotalCount'],
                 ],
                 'pageInfo' => [
-                    'type'        => new NonNullType(new PageInfoType()),
+                    'type' => new NonNullType(new PageInfoType()),
                     'description' => 'Information to aid in pagination.',
-                    'resolve'     => [__CLASS__, 'getPageInfo'],
+                    'resolve' => [__CLASS__, 'getPageInfo'],
                 ],
-                'edges'    => [
-                    'type'        => new ListType(self::edgeDefinition($type, $name, $config)),
+                'edges' => [
+                    'type' => new ListType(self::edgeDefinition($type, $name, $config)),
                     'description' => 'A list of edges.',
-                    'resolve'     => [__CLASS__, 'getEdges'],
+                    'resolve' => [__CLASS__, 'getEdges'],
                 ]
             ], $connectionFields)
         ]);
-
-        return $connectionType;
     }
 
-    public static function getTotalCount($value)
+    public static function getTotalCount(array $value)
     {
-        return isset($value['totalCount']) ? $value['totalCount'] : -1;
+        return $value['totalCount'] ?? -1;
     }
 
-    public static function getEdges($value)
+    public static function getEdges(array $value)
     {
-        return isset($value['edges']) ? $value['edges'] : null;
+        return $value['edges'] ?? null;
     }
 
-    public static function getPageInfo($value)
+    public static function getPageInfo(array $value)
     {
-        return isset($value['pageInfo']) ? $value['pageInfo'] : null;
+        return $value['pageInfo'] ?? null;
     }
 
-    public static function getNode($value)
+    public static function getNode(array $value)
     {
-        return isset($value['node']) ? $value['node'] : null;
+        return $value['node'] ?? null;
     }
 }
diff --git a/src/Relay/Field/GlobalIdField.php b/src/Relay/Field/GlobalIdField.php
index d9569e83..c4aec0e5 100644
--- a/src/Relay/Field/GlobalIdField.php
+++ b/src/Relay/Field/GlobalIdField.php
@@ -9,6 +9,7 @@
 namespace Youshido\GraphQL\Relay\Field;
 
 
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\AbstractField;
 use Youshido\GraphQL\Relay\Node;
@@ -23,31 +24,37 @@ class GlobalIdField extends AbstractField
 
     /**
      * @param string $typeName
+     * @throws ConfigurationException
      */
     public function __construct($typeName)
     {
         $this->typeName = $typeName;
 
         $config = [
-            'type'    => $this->getType(),
-            'name'    => $this->getName(),
-            'resolve' => [$this, 'resolve']
+            'type' => $this->getType(),
+            'name' => $this->getName(),
+            'resolve' => function ($value, array $args, ResolveInfo $info): ?string {
+                return $this->resolve($value, $args, $info);
+            }
         ];
 
         parent::__construct($config);
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'id';
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'The ID of an object';
     }
 
-    public function getType()
+    /**
+     * @throws ConfigurationException
+     */
+    public function getType(): NonNullType
     {
         return new NonNullType(new IdType());
     }
@@ -55,7 +62,7 @@ public function getType()
     /**
      * @inheritdoc
      */
-    public function resolve($value, array $args, ResolveInfo $info)
+    public function resolve($value, array $args, ResolveInfo $info): ?string
     {
         return $value ? Node::toGlobalId($this->typeName, $value['id']) : null;
     }
diff --git a/src/Relay/Field/NodeField.php b/src/Relay/Field/NodeField.php
index 449465f8..87898d47 100644
--- a/src/Relay/Field/NodeField.php
+++ b/src/Relay/Field/NodeField.php
@@ -10,6 +10,7 @@
 
 
 use Youshido\GraphQL\Config\Field\FieldConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\AbstractField;
 use Youshido\GraphQL\Field\InputField;
@@ -21,51 +22,49 @@
 
 class NodeField extends AbstractField
 {
+    protected FetcherInterface $fetcher;
 
-    /** @var  FetcherInterface */
-    protected $fetcher;
-
-    /** @var NodeInterfaceType */
-    protected $type;
+    protected NodeInterfaceType $type;
 
     public function __construct(FetcherInterface $fetcher)
     {
         $this->fetcher = $fetcher;
-        $this->type    = (new NodeInterfaceType())->setFetcher($this->fetcher);
+        $this->type = (new NodeInterfaceType())->setFetcher($this->fetcher);
 
-        parent::__construct([]);
+        parent::__construct();
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'node';
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'Fetches an object given its ID';
     }
 
-    public function build(FieldConfig $config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(FieldConfig $config): void
     {
         $config->addArgument(new InputField([
-            'name'        => 'id',
-            'type'        => new NonNullType(new IdType()),
+            'name' => 'id',
+            'type' => new NonNullType(new IdType()),
             'description' => 'The ID of an object'
         ]));
     }
 
-    public function getType()
+    public function getType(): mixed
     {
         return $this->type;
     }
 
-    public function resolve($value, array $args, ResolveInfo $info)
+    public function resolve($value, array $args, ResolveInfo $info): mixed
     {
         list($type, $id) = Node::fromGlobalId($args['id']);
 
         return $this->fetcher->resolveNode($type, $id);
     }
-
-
 }
diff --git a/src/Relay/Node.php b/src/Relay/Node.php
index 3e360333..cef53b49 100644
--- a/src/Relay/Node.php
+++ b/src/Relay/Node.php
@@ -8,6 +8,8 @@
 namespace Youshido\GraphQL\Relay;
 
 
+use InvalidArgumentException;
+
 class Node
 {
 
@@ -16,16 +18,18 @@ class Node
      *
      * @return array with type and id element
      */
-    public static function fromGlobalId($id)
+    public static function fromGlobalId($id): array
     {
-        $decoded = base64_decode($id, true);
+        $decoded = base64_decode((string)$id, true);
         if (!$decoded) {
-            throw new \InvalidArgumentException('ID must be a valid base 64 string');
+            throw new InvalidArgumentException('ID must be a valid base 64 string');
         }
+
         $decodedParts = explode(':', $decoded, 2);
         if (count($decodedParts) !== 2) {
-            throw new \InvalidArgumentException('ID was not correctly formed');
+            throw new InvalidArgumentException('ID was not correctly formed');
         }
+
         return $decodedParts;
     }
 
@@ -35,7 +39,7 @@ public static function fromGlobalId($id)
      *
      * @return string global id
      */
-    public static function toGlobalId($typeName, $id)
+    public static function toGlobalId($typeName, $id): string
     {
         return base64_encode(implode(':', [$typeName, $id]));
     }
diff --git a/src/Relay/NodeInterfaceType.php b/src/Relay/NodeInterfaceType.php
index 045726ee..5f50e9d5 100644
--- a/src/Relay/NodeInterfaceType.php
+++ b/src/Relay/NodeInterfaceType.php
@@ -9,6 +9,8 @@
 namespace Youshido\GraphQL\Relay;
 
 
+use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Relay\Fetcher\FetcherInterface;
 use Youshido\GraphQL\Relay\Field\GlobalIdField;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
@@ -19,23 +21,23 @@ class NodeInterfaceType extends AbstractInterfaceType
     /** @var  FetcherInterface */ //todo: maybe there are better solution
     protected $fetcher;
 
-    public function getName()
+    public function getName(): string
     {
         return 'NodeInterface';
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(InterfaceTypeConfig $config): void
     {
         $config->addField(new GlobalIdField('NodeInterface'));
     }
 
     public function resolveType($object)
     {
-        if ($this->fetcher) {
-            return $this->fetcher->resolveType($object);
-        }
+        return $this->fetcher?->resolveType($object);
 
-        return null;
     }
 
     /**
@@ -48,10 +50,8 @@ public function getFetcher()
 
     /**
      * @param FetcherInterface $fetcher
-     *
-     * @return NodeInterfaceType
      */
-    public function setFetcher($fetcher)
+    public function setFetcher($fetcher): static
     {
         $this->fetcher = $fetcher;
 
diff --git a/src/Relay/RelayMutation.php b/src/Relay/RelayMutation.php
index 501d4151..ac51ae09 100644
--- a/src/Relay/RelayMutation.php
+++ b/src/Relay/RelayMutation.php
@@ -8,6 +8,7 @@
 namespace Youshido\GraphQL\Relay;
 
 
+use Exception;
 use Youshido\GraphQL\Execution\ResolveInfo;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Field\InputField;
@@ -21,28 +22,25 @@ class RelayMutation
 {
 
     /**
-     * @param string                   $name
-     * @param array                    $args
+     * @param string $name
      * @param AbstractObjectType|array $output
-     * @param callable                 $resolveFunction
      *
-     * @return Field
      *
-     * @throws \Exception
+     * @throws Exception
      */
-    public static function buildMutation($name, array $args, $output, callable $resolveFunction)
+    public static function buildMutation($name, array $args, $output, callable $resolveFunction): Field
     {
         if (!is_array($output) || (is_object($output) && !($output instanceof AbstractObjectType))) {
-            throw new \Exception('Output can be instance of AbstractObjectType or array of fields');
+            throw new Exception('Output can be instance of AbstractObjectType or array of fields');
         }
 
         return new Field([
-            'name'    => $name,
-            'args'    => [
+            'name' => $name,
+            'args' => [
                 new InputField([
                     'name' => 'input',
                     'type' => new NonNullType(new InputObjectType([
-                        'name'   => ucfirst($name) . 'Input',
+                        'name' => ucfirst($name) . 'Input',
                         'fields' => array_merge(
                             $args,
                             [new InputField(['name' => 'clientMutationId', 'type' => new NonNullType(new StringType())])]
@@ -50,22 +48,21 @@ public static function buildMutation($name, array $args, $output, callable $reso
                     ]))
                 ])
             ],
-            'type'    => new ObjectType([
+            'type' => new ObjectType([
                 'fields' => is_object($output) ? $output : array_merge(
                     $output,
                     [new Field(['name' => 'clientMutationId', 'type' => new NonNullType(new StringType())])]
                 ),
-                'name'   => ucfirst($name) . 'Payload'
+                'name' => ucfirst($name) . 'Payload'
             ]),
-            'resolve' => function ($value, $args, ResolveInfo $info) use ($resolveFunction) {
+            'resolve' => static function ($value, array $args, ResolveInfo $info) use ($resolveFunction) {
                 $resolveValue = $resolveFunction($value, $args['input'], $args, $info);
-
                 if (is_object($resolveValue)) {
                     $resolveValue->clientMutationId = $args['input']['clientMutationId'];
                 } elseif (is_array($resolveValue)) {
                     $resolveValue['clientMutationId'] = $args['input']['clientMutationId'];
                 }
-
+                
                 return $resolveValue;
             }
         ]);
diff --git a/src/Relay/Type/PageInfoType.php b/src/Relay/Type/PageInfoType.php
index 74d786fd..c3606cc2 100644
--- a/src/Relay/Type/PageInfoType.php
+++ b/src/Relay/Type/PageInfoType.php
@@ -9,6 +9,8 @@
 namespace Youshido\GraphQL\Relay\Type;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\BooleanType;
@@ -16,29 +18,32 @@
 
 class PageInfoType extends AbstractObjectType
 {
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addFields([
-            'hasNextPage'     => [
-                'type'        => new NonNullType(new BooleanType()),
+            'hasNextPage' => [
+                'type' => new NonNullType(new BooleanType()),
                 'description' => 'When paginating forwards, are there more items?'
             ],
             'hasPreviousPage' => [
-                'type'        => new NonNullType(new BooleanType()),
+                'type' => new NonNullType(new BooleanType()),
                 'description' => 'When paginating backwards, are there more items?'
             ],
-            'startCursor'     => [
-                'type'        => new StringType(),
+            'startCursor' => [
+                'type' => new StringType(),
                 'description' => 'When paginating backwards, the cursor to continue.'
             ],
-            'endCursor'       => [
-                'type'        => new StringType(),
+            'endCursor' => [
+                'type' => new StringType(),
                 'description' => 'When paginating forwards, the cursor to continue.'
             ],
         ]);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return "Information about pagination in a connection.";
     }
diff --git a/src/Schema/AbstractSchema.php b/src/Schema/AbstractSchema.php
index 349cdd84..5d64145c 100644
--- a/src/Schema/AbstractSchema.php
+++ b/src/Schema/AbstractSchema.php
@@ -10,25 +10,30 @@
 
 
 use Youshido\GraphQL\Config\Schema\SchemaConfig;
-use Youshido\GraphQL\Type\SchemaTypesList;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\SchemaDirectivesList;
+use Youshido\GraphQL\Type\SchemaTypesList;
 
 abstract class AbstractSchema
 {
 
-    /** @var SchemaConfig */
-    protected $config;
+    protected SchemaConfig $config;
 
-    public function __construct($config = [])
+    /**
+     * @throws ConfigurationException
+     */
+    public function __construct(array $config = [])
     {
         if (!array_key_exists('query', $config)) {
             $config['query'] = new InternalSchemaQueryObject(['name' => $this->getName($config) . 'Query']);
         }
+
         if (!array_key_exists('mutation', $config)) {
             $config['mutation'] = new InternalSchemaMutationObject(['name' => $this->getName($config) . 'Mutation']);
         }
+
         if (!array_key_exists('types', $config)) {
-          $config['types'] = [];
+            $config['types'] = [];
         }
 
         $this->config = new SchemaConfig($config, $this);
@@ -38,12 +43,18 @@ public function __construct($config = [])
 
     abstract public function build(SchemaConfig $config);
 
-    public function addQueryField($field, $fieldInfo = null)
+    /**
+     * @throws ConfigurationException
+     */
+    public function addQueryField($field, $fieldInfo = null): void
     {
         $this->getQueryType()->addField($field, $fieldInfo);
     }
 
-    public function addMutationField($field, $fieldInfo = null)
+    /**
+     * @throws ConfigurationException
+     */
+    public function addMutationField($field, $fieldInfo = null): void
     {
         $this->getMutationType()->addField($field, $fieldInfo);
     }
@@ -74,10 +85,10 @@ public function getDirectiveList()
         return $this->config->getDirectiveList();
     }
 
-    public function getName($config)
+    public function getName(array $config)
     {
         $defaultName = 'RootSchema';
 
-        return isset($config["name"])? $config["name"] : $defaultName;
+        return $config["name"] ?? $defaultName;
     }
 }
diff --git a/src/Schema/InternalSchemaMutationObject.php b/src/Schema/InternalSchemaMutationObject.php
index a31e112b..89596402 100644
--- a/src/Schema/InternalSchemaMutationObject.php
+++ b/src/Schema/InternalSchemaMutationObject.php
@@ -9,11 +9,12 @@
 namespace Youshido\GraphQL\Schema;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 
 class InternalSchemaMutationObject extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
     }
 
diff --git a/src/Schema/InternalSchemaQueryObject.php b/src/Schema/InternalSchemaQueryObject.php
index bf98d9e7..bc9cef26 100644
--- a/src/Schema/InternalSchemaQueryObject.php
+++ b/src/Schema/InternalSchemaQueryObject.php
@@ -9,11 +9,12 @@
 namespace Youshido\GraphQL\Schema;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 
 class InternalSchemaQueryObject extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
     }
 
diff --git a/src/Schema/Schema.php b/src/Schema/Schema.php
index b6cfb45a..edc212ac 100644
--- a/src/Schema/Schema.php
+++ b/src/Schema/Schema.php
@@ -12,7 +12,7 @@
 
 final class Schema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
     }
 }
diff --git a/src/Type/AbstractInterfaceTypeInterface.php b/src/Type/AbstractInterfaceTypeInterface.php
index 2d76ef59..d84e4be0 100644
--- a/src/Type/AbstractInterfaceTypeInterface.php
+++ b/src/Type/AbstractInterfaceTypeInterface.php
@@ -13,8 +13,6 @@ interface AbstractInterfaceTypeInterface
 {
     /**
      * @param $object object from resolve function
-     *
-     * @return AbstractType
      */
-    public function resolveType($object);
+    public function resolveType(object $object): ?AbstractType;
 }
diff --git a/src/Type/AbstractType.php b/src/Type/AbstractType.php
index 646edbb8..e583f5c4 100644
--- a/src/Type/AbstractType.php
+++ b/src/Type/AbstractType.php
@@ -8,54 +8,42 @@
 
 namespace Youshido\GraphQL\Type;
 
-
-use Youshido\GraphQL\Type\Object\AbstractObjectType;
-
 abstract class AbstractType implements TypeInterface
 {
 
-    protected $lastValidationError = null;
+    protected $lastValidationError;
 
-    public function isCompositeType()
+    public function isCompositeType(): bool
     {
         return false;
     }
 
-    /**
-     * @return AbstractType
-     */
-    public function getType()
+    public function getType(): mixed
     {
         return $this;
     }
 
-    /**
-     * @return AbstractType
-     */
-    public function getNamedType()
+    public function getNamedType(): mixed
     {
         return $this->getType();
     }
 
-    /**
-     * @return AbstractType|AbstractObjectType
-     */
-    public function getNullableType()
+    public function getNullableType(): mixed
     {
         return $this;
     }
 
-    public function getValidationError($value = null)
+    public function getValidationError($value = null): ?string
     {
         return $this->lastValidationError;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return true;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): mixed
     {
         return $value;
     }
@@ -65,18 +53,18 @@ public function parseInputValue($value)
         return $this->parseValue($value);
     }
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         return $value;
     }
 
-    public function isInputType()
+    public function isInputType(): bool
     {
         return false;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
-        return $this->getName();
+        return $this->getName() ?? '';
     }
 }
diff --git a/src/Type/CompositeTypeInterface.php b/src/Type/CompositeTypeInterface.php
index 3e631676..8e074be2 100644
--- a/src/Type/CompositeTypeInterface.php
+++ b/src/Type/CompositeTypeInterface.php
@@ -7,11 +7,8 @@
  * @author Alexandr Viniychuk <a@viniychuk.com>
  * created: 3:48 PM 4/29/16
  */
+
 interface CompositeTypeInterface
 {
-
-    /**
-     * @return AbstractType
-     */
-    public function getTypeOf();
+    public function getTypeOf(): mixed;
 }
diff --git a/src/Type/Enum/AbstractEnumType.php b/src/Type/Enum/AbstractEnumType.php
index 97b764c7..4679125d 100644
--- a/src/Type/Enum/AbstractEnumType.php
+++ b/src/Type/Enum/AbstractEnumType.php
@@ -10,6 +10,7 @@
 
 use Youshido\GraphQL\Config\Object\EnumTypeConfig;
 use Youshido\GraphQL\Config\Traits\ConfigAwareTrait;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 use Youshido\GraphQL\Type\TypeMap;
@@ -17,16 +18,17 @@
 abstract class AbstractEnumType extends AbstractType
 {
 
-    use AutoNameTrait, ConfigAwareTrait;
+    use AutoNameTrait;
+    use ConfigAwareTrait;
 
     /**
      * ObjectType constructor.
-     * @param $config
+     * @throws ConfigurationException
      */
-    public function __construct($config = [])
+    public function __construct(array $config = [])
     {
-        if (empty($config)) {
-            $config['name']   = $this->getName();
+        if ($config === []) {
+            $config['name'] = $this->getName();
             $config['values'] = $this->getValues();
         }
 
@@ -36,19 +38,20 @@ public function __construct($config = [])
     /**
      * @return String predefined type kind
      */
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_ENUM;
     }
 
     /**
      * @param $value mixed
-     *
-     * @return bool
      */
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
-        if (is_null($value)) return true;
+        if (is_null($value)) {
+            return true;
+        }
+
         foreach ($this->getConfig()->get('values') as $item) {
             if ($value === $item['name'] || $value === $item['value']) {
                 return true;
@@ -58,20 +61,17 @@ public function isValidValue($value)
         return false;
     }
 
-    public function getValidationError($value = null)
+    public function getValidationError($value = null): ?string
     {
-        $allowedValues             = array_map(function (array $value) {
+        $allowedValues = array_map(static function (array $value): string {
             return sprintf('%s (%s)', $value['name'], $value['value']);
         }, $this->getConfig()->get('values'));
         return sprintf('Value must be one of the allowed ones: %s', implode(', ', $allowedValues));
     }
 
-    /**
-     * @return array
-     */
-    abstract public function getValues();
+    abstract public function getValues(): array;
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         foreach ($this->getConfig()->get('values') as $valueItem) {
             if ($value === $valueItem['value']) {
@@ -82,7 +82,7 @@ public function serialize($value)
         return null;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): mixed
     {
         foreach ($this->getConfig()->get('values') as $valueItem) {
             if ($value === $valueItem['name']) {
diff --git a/src/Type/Enum/EnumType.php b/src/Type/Enum/EnumType.php
index 63ce6f9c..a16475c7 100644
--- a/src/Type/Enum/EnumType.php
+++ b/src/Type/Enum/EnumType.php
@@ -14,10 +14,11 @@ final class EnumType extends AbstractEnumType
 
     public function __construct(array $config)
     {
+        parent::__construct($config);
         $this->config = new EnumTypeConfig($config, $this, true);
     }
 
-    public function getValues()
+    public function getValues(): array
     {
         return $this->getConfig()->getValues();
     }
diff --git a/src/Type/InputObject/AbstractInputObjectType.php b/src/Type/InputObject/AbstractInputObjectType.php
index 15312d28..1ea74fdb 100644
--- a/src/Type/InputObject/AbstractInputObjectType.php
+++ b/src/Type/InputObject/AbstractInputObjectType.php
@@ -9,7 +9,10 @@
 namespace Youshido\GraphQL\Type\InputObject;
 
 
+use Exception;
+use Youshido\GraphQL\Config\AbstractConfig;
 use Youshido\GraphQL\Config\Object\InputObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\InputFieldInterface;
 use Youshido\GraphQL\Parser\Ast\ArgumentValue\InputObject;
 use Youshido\GraphQL\Parser\Ast\ArgumentValue\Variable;
@@ -21,11 +24,12 @@
 abstract class AbstractInputObjectType extends AbstractType
 {
 
-    use AutoNameTrait, FieldsAwareObjectTrait;
+    use AutoNameTrait;
+    use FieldsAwareObjectTrait;
 
     protected $isBuilt = false;
 
-    public function getConfig()
+    public function getConfig(): InputObjectTypeConfig
     {
         if (!$this->isBuilt) {
             $this->isBuilt = true;
@@ -35,6 +39,9 @@ public function getConfig()
         return $this->config;
     }
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct($config = [])
     {
         if (empty($config)) {
@@ -42,6 +49,7 @@ public function __construct($config = [])
                 'name' => $this->getName()
             ];
         }
+
         $this->config = new InputObjectTypeConfig($config, $this);
     }
 
@@ -50,7 +58,7 @@ public function __construct($config = [])
      */
     abstract public function build($config);
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         if ($value instanceof InputObject) {
             $value = $value->getValue();
@@ -64,8 +72,8 @@ public function isValidValue($value)
             return false;
         }
 
-        $typeConfig     = $this->getConfig();
-        $requiredFields = array_filter($typeConfig->getFields(), function (InputFieldInterface $field) {
+        $typeConfig = $this->getConfig();
+        $requiredFields = array_filter($typeConfig->getFields(), static function (InputFieldInterface $field): bool {
             return $field->getType()->getKind() == TypeMap::KIND_NON_NULL;
         });
 
@@ -77,7 +85,7 @@ public function isValidValue($value)
 
             $field = $typeConfig->getField($valueKey);
             if (!$field->getType()->isValidValue($valueItem)) {
-                $error                     = $field->getType()->getValidationError($valueItem) ?: '(no details available)';
+                $error = $field->getType()->getValidationError($valueItem) ?: '(no details available)';
                 $this->lastValidationError = sprintf('Not valid type for field "%s" in input type "%s": %s', $field->getName(), $this->getName(), $error);
                 return false;
             }
@@ -86,27 +94,34 @@ public function isValidValue($value)
                 unset($requiredFields[$valueKey]);
             }
         }
-        if (count($requiredFields)) {
+
+        if ($requiredFields !== []) {
             $this->lastValidationError = sprintf('%s %s required on %s', implode(', ', array_keys($requiredFields)), count($requiredFields) > 1 ? 'are' : 'is', $typeConfig->getName());
         }
 
-        return !(count($requiredFields) > 0);
+        return count($requiredFields) <= 0;
     }
 
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_INPUT_OBJECT;
     }
 
-    public function isInputType()
+    public function isInputType(): bool
     {
         return true;
     }
 
-    public function parseValue($value)
+    /**
+     * @throws Exception
+     */
+    public function parseValue($value): mixed
     {
-        if (is_null($value)) return null;
-        if($value instanceof InputObject) {
+        if (is_null($value)) {
+            return null;
+        }
+
+        if ($value instanceof InputObject) {
             $value = $value->getValue();
         }
 
@@ -117,8 +132,9 @@ public function parseValue($value)
             }
 
             if (!($inputField = $typeConfig->getField($valueKey))) {
-                throw new \Exception(sprintf('Invalid field "%s" on %s', $valueKey, $typeConfig->getName()));
+                throw new Exception(sprintf('Invalid field "%s" on %s', $valueKey, $typeConfig->getName()));
             }
+
             $value[$valueKey] = $inputField->getType()->parseValue($item);
         }
 
diff --git a/src/Type/InputObject/InputObjectType.php b/src/Type/InputObject/InputObjectType.php
index a44fc03b..8ee2f963 100644
--- a/src/Type/InputObject/InputObjectType.php
+++ b/src/Type/InputObject/InputObjectType.php
@@ -9,21 +9,26 @@
 namespace Youshido\GraphQL\Type\InputObject;
 
 use Youshido\GraphQL\Config\Object\InputObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 
 final class InputObjectType extends AbstractInputObjectType
 {
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct($config)
     {
+        parent::__construct($config);
         $this->config = new InputObjectTypeConfig($config, $this, true);
     }
 
     /**
      * @inheritdoc
-     * 
+     *
      * @codeCoverageIgnore
      */
-    public function build($config)
+    public function build($config): void
     {
     }
 }
diff --git a/src/Type/InputTypeInterface.php b/src/Type/InputTypeInterface.php
index 1fd7eab1..278c3f39 100644
--- a/src/Type/InputTypeInterface.php
+++ b/src/Type/InputTypeInterface.php
@@ -9,50 +9,41 @@
 namespace Youshido\GraphQL\Type;
 
 
-use Youshido\GraphQL\Config\AbstractConfig;
-
 interface InputTypeInterface
 {
     /**
-     * @return String type name
+     * @return string|null type name
      */
-    public function getName();
+    public function getName(): ?string;
 
     /**
      * @return String predefined type kind
      */
-    public function getKind();
+    public function getKind(): string;
 
     /**
      * @return String type description
      */
-    public function getDescription();
+    public function getDescription(): string;
 
     /**
      * Coercing value received as input to current type
      *
      * @param $value
-     * @return mixed
      */
-    public function parseValue($value);
+    public function parseValue($value): mixed;
 
     /**
      * Coercing result to current type
      *
      * @param $value
-     * @return mixed
      */
-    public function serialize($value);
+    public function serialize($value): mixed;
 
     /**
      * @param $value mixed
-     *
-     * @return bool
      */
-    public function isValidValue($value);
+    public function isValidValue(mixed $value): bool;
 
-    /**
-     * @return AbstractConfig
-     */
     public function getConfig();
 }
\ No newline at end of file
diff --git a/src/Type/InterfaceType/AbstractInterfaceType.php b/src/Type/InterfaceType/AbstractInterfaceType.php
index 6e26a354..e4882ef7 100644
--- a/src/Type/InterfaceType/AbstractInterfaceType.php
+++ b/src/Type/InterfaceType/AbstractInterfaceType.php
@@ -10,6 +10,7 @@
 
 
 use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 use Youshido\GraphQL\Type\Traits\FieldsAwareObjectTrait;
@@ -18,11 +19,12 @@
 
 abstract class AbstractInterfaceType extends AbstractType
 {
-    use FieldsAwareObjectTrait, AutoNameTrait;
+    use FieldsAwareObjectTrait;
+    use AutoNameTrait;
 
-    protected $isBuilt = false;
+    protected bool $isBuilt = false;
 
-    public function getConfig()
+    public function getConfig(): InterfaceTypeConfig
     {
         if (!$this->isBuilt) {
             $this->isBuilt = true;
@@ -35,11 +37,11 @@ public function getConfig()
     /**
      * ObjectType constructor.
      *
-     * @param $config
+     * @throws ConfigurationException
      */
-    public function __construct($config = [])
+    public function __construct(array $config = [])
     {
-        if (empty($config)) {
+        if ($config === []) {
             $config['name'] = $this->getName();
         }
 
@@ -48,31 +50,28 @@ public function __construct($config = [])
 
     abstract public function resolveType($object);
 
-    /**
-     * @param InterfaceTypeConfig $config
-     */
-    abstract public function build($config);
+    abstract public function build(InterfaceTypeConfig $config);
 
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_INTERFACE;
     }
 
-    public function getNamedType()
+    public function getNamedType(): AbstractInterfaceType|static
     {
         return $this;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_array($value) || is_null($value) || is_object($value);
     }
 
     /**
-     * @return TypeInterface[] an array of types that implement this interface. Used mainly for introspection and 
+     * @return TypeInterface[] an array of types that implement this interface. Used mainly for introspection and
      *                         documentation generation.
      */
-    public function getImplementations()
+    public function getImplementations(): array
     {
         return [];
     }
diff --git a/src/Type/InterfaceType/InterfaceType.php b/src/Type/InterfaceType/InterfaceType.php
index 7f4154e8..9fea674f 100644
--- a/src/Type/InterfaceType/InterfaceType.php
+++ b/src/Type/InterfaceType/InterfaceType.php
@@ -9,24 +9,29 @@
 
 
 use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 
 final class InterfaceType extends AbstractInterfaceType
 {
 
-    public function __construct($config = [])
+    public function __construct(array $config = [])
     {
+        parent::__construct($config);
         $this->config = new InterfaceTypeConfig($config, $this, true);
     }
 
     /**
      * @inheritdoc
-     * 
+     *
      * @codeCoverageIgnore
      */
-    public function build($config)
+    public function build(InterfaceTypeConfig $config): void
     {
     }
 
+    /**
+     * @throws ConfigurationException
+     */
     public function resolveType($object)
     {
         return $this->getConfig()->resolveType($object);
diff --git a/src/Type/ListType/AbstractListType.php b/src/Type/ListType/AbstractListType.php
index 94aedb37..6c6f9839 100644
--- a/src/Type/ListType/AbstractListType.php
+++ b/src/Type/ListType/AbstractListType.php
@@ -7,35 +7,32 @@
 
 namespace Youshido\GraphQL\Type\ListType;
 
-
+use Exception;
+use Traversable;
 use Youshido\GraphQL\Config\Object\ListTypeConfig;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
+use Youshido\GraphQL\Type\AbstractType;
 use Youshido\GraphQL\Type\CompositeTypeInterface;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\TypeMap;
 
 abstract class AbstractListType extends AbstractObjectType implements CompositeTypeInterface
 {
-    /**
-     * @var ListTypeConfig
-     */
     protected $config;
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct()
     {
+        parent::__construct();
         $this->config = new ListTypeConfig(['itemType' => $this->getItemType()], $this);
     }
 
-    /**
-     * @return AbstractObjectType
-     */
-    abstract public function getItemType();
+    abstract public function getItemType(): mixed;
 
-    /**
-     * @param mixed $value
-     *
-     * @return bool
-     */
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         if (!$this->isIterable($value)) {
             return false;
@@ -46,14 +43,16 @@ public function isValidValue($value)
 
     /**
      * @param $value
-     * @param bool $returnValue
-     *
-     * @return bool
+     * @return mixed - true/false or type of the returned value if $returnValue is true
      */
-    protected function validList($value, $returnValue = false)
+    protected function validList($value, bool $returnValue = false): mixed
     {
         $itemType = $this->config->get('itemType');
 
+        if (empty($itemType)) {
+            return false;
+        }
+
         if ($value && $itemType->isInputType()) {
             foreach ($value as $item) {
                 if (!$itemType->isValidValue($item)) {
@@ -68,54 +67,60 @@ protected function validList($value, $returnValue = false)
     /**
      * @inheritdoc
      */
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
     }
 
-    public function isCompositeType()
+    public function isCompositeType(): bool
     {
         return true;
     }
 
-    public function getNamedType()
+    public function getNamedType(): mixed
     {
         return $this->getItemType();
     }
 
-    final public function getKind()
+    final public function getKind(): string
     {
         return TypeMap::KIND_LIST;
     }
 
-    public function getTypeOf()
+    public function getTypeOf(): AbstractType
     {
         return $this->getNamedType();
     }
 
-    public function parseValue($value)
+    /**
+     * @throws Exception
+     */
+    public function parseValue($value): mixed
     {
-        foreach ((array) $value as $keyValue => $valueItem) {
+        foreach ((array)$value as $keyValue => $valueItem) {
             $value[$keyValue] = $this->getItemType()->parseValue($valueItem);
         }
 
         return $value;
     }
 
-    public function getValidationError($value = null)
+    public function getValidationError($value = null): ?string
     {
         if (!$this->isIterable($value)) {
             return 'The value is not an iterable.';
         }
+
+        if (empty($this->config->get('itemType'))) {
+            return 'itemType is empty.';
+        }
+
         return $this->config->get('itemType')->getValidationError($this->validList($value, true));
     }
 
     /**
      * @param $value
-     *
-     * @return bool
      */
-    protected function isIterable($value)
+    protected function isIterable($value): bool
     {
-        return null === $value || is_array($value) || ($value instanceof \Traversable);
+        return null === $value || is_array($value) || ($value instanceof Traversable);
     }
 }
diff --git a/src/Type/ListType/ListType.php b/src/Type/ListType/ListType.php
index 20244c38..cbb9b55a 100644
--- a/src/Type/ListType/ListType.php
+++ b/src/Type/ListType/ListType.php
@@ -10,21 +10,28 @@
 
 
 use Youshido\GraphQL\Config\Object\ListTypeConfig;
+use Youshido\GraphQL\Type\Enum\AbstractEnumType;
+use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
+use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
+use Youshido\GraphQL\Type\NonNullType;
+use Youshido\GraphQL\Type\Object\AbstractObjectType;
+use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
 
 final class ListType extends AbstractListType
 {
 
     public function __construct($itemType)
     {
+        parent::__construct();
         $this->config = new ListTypeConfig(['itemType' => $itemType], $this, true);
     }
 
-    public function getItemType()
+    public function getItemType(): mixed
     {
         return $this->getConfig()->get('itemType');
     }
 
-    public function getName()
+    public function getName(): ?string
     {
         return null;
     }
diff --git a/src/Type/NonNullType.php b/src/Type/NonNullType.php
index abe67bf0..763efd96 100644
--- a/src/Type/NonNullType.php
+++ b/src/Type/NonNullType.php
@@ -16,20 +16,20 @@ final class NonNullType extends AbstractType implements CompositeTypeInterface
 {
     use ConfigAwareTrait;
 
-    private $_typeOf;
+    private mixed $_typeOf;
 
     /**
      * NonNullType constructor.
      *
-     * @param AbstractType|string $fieldType
      *
      * @throws ConfigurationException
      */
-    public function __construct($fieldType)
+    public function __construct(string|AbstractType $fieldType)
     {
         if (!TypeService::isGraphQLType($fieldType)) {
             throw new ConfigurationException('NonNullType accepts only GraphpQL Types as argument');
         }
+
         if (TypeService::isScalarType($fieldType)) {
             $fieldType = TypeFactory::getScalarType($fieldType);
         }
@@ -37,12 +37,12 @@ public function __construct($fieldType)
         $this->_typeOf = $fieldType;
     }
 
-    public function getName()
+    public function getName(): ?string
     {
         return null;
     }
 
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_NON_NULL;
     }
@@ -52,7 +52,7 @@ public function resolve($value)
         return $value;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         if ($value === null) {
             return false;
@@ -61,43 +61,42 @@ public function isValidValue($value)
         return $this->getNullableType()->isValidValue($value);
     }
 
-    public function isCompositeType()
+    public function isCompositeType(): bool
     {
         return true;
     }
 
-    public function isInputType()
+    public function isInputType(): bool
     {
         return true;
     }
 
-    public function getNamedType()
+    public function getNamedType(): mixed
     {
         return $this->getTypeOf();
     }
 
-    public function getNullableType()
+    public function getNullableType(): mixed
     {
         return $this->getTypeOf();
     }
 
-    public function getTypeOf()
+    public function getTypeOf(): mixed
     {
         return $this->_typeOf;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): mixed
     {
         return $this->getNullableType()->parseValue($value);
     }
 
-    public function getValidationError($value = null)
+    public function getValidationError($value = null): ?string
     {
         if ($value === null) {
             return 'Field must not be NULL';
         }
+
         return $this->getNullableType()->getValidationError($value);
     }
-
-
-}
+}
\ No newline at end of file
diff --git a/src/Type/Object/AbstractMutationObjectType.php b/src/Type/Object/AbstractMutationObjectType.php
index b40387ac..3d8cb570 100644
--- a/src/Type/Object/AbstractMutationObjectType.php
+++ b/src/Type/Object/AbstractMutationObjectType.php
@@ -7,10 +7,14 @@
 
 namespace Youshido\GraphQL\Type\Object;
 
+use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
+use Youshido\GraphQL\Type\NonNullType;
+use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
+
 abstract class AbstractMutationObjectType extends AbstractObjectType
 {
 
-    public function getType()
+    public function getType(): NonNullType|AbstractObjectType|AbstractScalarType|AbstractInputObjectType|null|static
     {
         return $this->getOutputType();
     }
diff --git a/src/Type/Object/AbstractObjectType.php b/src/Type/Object/AbstractObjectType.php
index 4cdc49d0..48eb339a 100644
--- a/src/Type/Object/AbstractObjectType.php
+++ b/src/Type/Object/AbstractObjectType.php
@@ -9,9 +9,15 @@
 namespace Youshido\GraphQL\Type\Object;
 
 
+use InvalidArgumentException;
 use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\AbstractType;
+use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
+use Youshido\GraphQL\Type\Enum\AbstractEnumType;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
+use Youshido\GraphQL\Type\NonNullType;
+use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
 use Youshido\GraphQL\Type\Traits\FieldsArgumentsAwareObjectTrait;
 use Youshido\GraphQL\Type\TypeMap;
@@ -22,11 +28,12 @@
  */
 abstract class AbstractObjectType extends AbstractType
 {
-    use AutoNameTrait, FieldsArgumentsAwareObjectTrait;
+    use AutoNameTrait;
+    use FieldsArgumentsAwareObjectTrait;
 
-    protected $isBuilt = false;
+    protected bool $isBuilt = false;
 
-    public function getConfig()
+    public function getConfig(): ObjectTypeConfig
     {
         if (!$this->isBuilt) {
             $this->isBuilt = true;
@@ -38,54 +45,50 @@ public function getConfig()
 
     /**
      * ObjectType constructor.
-     * @param $config
+     * @throws ConfigurationException
      */
     public function __construct(array $config = [])
     {
-        if (empty($config)) {
-            $config['name']       = $this->getName();
+        if ($config === []) {
+            $config['name'] = $this->getName();
             $config['interfaces'] = $this->getInterfaces();
         }
 
         $this->config = new ObjectTypeConfig($config, $this);
     }
 
-    final public function serialize($value)
+    final public function serialize($value): mixed
     {
-        throw new \InvalidArgumentException('You can not serialize object value directly');
+        throw new InvalidArgumentException('You can not serialize object value directly');
     }
 
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_OBJECT;
     }
 
-    public function getType()
+    public function getType(): mixed
     {
         return $this->getConfigValue('type', $this);
     }
 
-    public function getNamedType()
+    public function getNamedType(): mixed
     {
         return $this;
     }
 
-    /**
-     * @param ObjectTypeConfig $config
-     */
-    abstract public function build($config);
+    abstract public function build(ObjectTypeConfig $config);
 
     /**
      * @return AbstractInterfaceType[]
      */
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return $this->getConfigValue('interfaces', []);
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_array($value) || is_null($value) || is_object($value);
     }
-
 }
diff --git a/src/Type/Object/ObjectType.php b/src/Type/Object/ObjectType.php
index e3692500..f9118f17 100644
--- a/src/Type/Object/ObjectType.php
+++ b/src/Type/Object/ObjectType.php
@@ -9,23 +9,30 @@
 namespace Youshido\GraphQL\Type\Object;
 
 use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 
 final class ObjectType extends AbstractObjectType
 {
 
+    /**
+     * @throws ConfigurationException
+     */
     public function __construct(array $config)
     {
+        parent::__construct($config);
         $this->config = new ObjectTypeConfig($config, $this, true);
     }
 
     /**
      * @inheritdoc
-     * 
+     *
      * @codeCoverageIgnore
      */
-    public function build($config) { }
+    public function build(ObjectTypeConfig $config): void
+    {
+    }
 
-    public function getName()
+    public function getName(): ?string
     {
         return $this->getConfigValue('name');
     }
diff --git a/src/Type/Scalar/AbstractScalarType.php b/src/Type/Scalar/AbstractScalarType.php
index 415cad2e..6a7f8390 100644
--- a/src/Type/Scalar/AbstractScalarType.php
+++ b/src/Type/Scalar/AbstractScalarType.php
@@ -16,24 +16,24 @@ abstract class AbstractScalarType extends AbstractType
 {
     use ConfigAwareTrait;
 
-    public function getName()
+    public function getName(): string
     {
         $className = get_class($this);
 
         return substr($className, strrpos($className, '\\') + 1, -4);
     }
 
-    final public function getKind()
+    final public function getKind(): string
     {
         return TypeMap::KIND_SCALAR;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): mixed
     {
         return $this->serialize($value);
     }
 
-    public function isInputType()
+    public function isInputType(): bool
     {
         return true;
     }
diff --git a/src/Type/Scalar/BooleanType.php b/src/Type/Scalar/BooleanType.php
index 8c0813c7..5c05fee2 100644
--- a/src/Type/Scalar/BooleanType.php
+++ b/src/Type/Scalar/BooleanType.php
@@ -11,19 +11,21 @@
 
 class BooleanType extends AbstractScalarType
 {
-    public function getName()
+    public function getName(): string
     {
         return 'Boolean';
     }
 
-    public function serialize($value)
+    public function serialize($value): ?bool
     {
         if ($value === null) {
             return null;
         }
+
         if ($value === 'true') {
             return true;
         }
+
         if ($value === 'false') {
             return false;
         }
@@ -31,12 +33,12 @@ public function serialize($value)
         return (bool)$value;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_null($value) || is_bool($value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'The `Boolean` scalar type represents `true` or `false`.';
     }
diff --git a/src/Type/Scalar/DateTimeType.php b/src/Type/Scalar/DateTimeType.php
index 324fa505..0a8aa088 100644
--- a/src/Type/Scalar/DateTimeType.php
+++ b/src/Type/Scalar/DateTimeType.php
@@ -8,6 +8,9 @@
 
 namespace Youshido\GraphQL\Type\Scalar;
 
+use DateTime;
+use DateTimeInterface;
+
 class DateTimeType extends AbstractScalarType
 {
 
@@ -18,42 +21,42 @@ public function __construct($format = 'Y-m-d H:i:s')
         $this->format = $format;
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'DateTime';
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
-        if ((is_object($value) && $value instanceof \DateTimeInterface) || is_null($value)) {
+        if (($value instanceof DateTimeInterface) || is_null($value)) {
             return true;
-        } else if (is_string($value)) {
+        } elseif (is_string($value)) {
             $date = $this->createFromFormat($value);
         } else {
             $date = null;
         }
 
-        return $date ? true : false;
+        return (bool)$date;
     }
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         $date = null;
 
         if (is_string($value)) {
             $date = $this->createFromFormat($value);
-        } elseif ($value instanceof \DateTimeInterface) {
+        } elseif ($value instanceof DateTimeInterface) {
             $date = $value;
         }
 
         return $date ? $date->format($this->format) : null;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): bool|null|DateTimeInterface|DateTime
     {
         if (is_string($value)) {
             $date = $this->createFromFormat($value);
-        } elseif ($value instanceof \DateTimeInterface) {
+        } elseif ($value instanceof DateTimeInterface) {
             $date = $value;
         } else {
             $date = false;
@@ -62,12 +65,12 @@ public function parseValue($value)
         return $date ?: null;
     }
 
-    private function createFromFormat($value)
+    private function createFromFormat(string $value): DateTime|bool
     {
-        return \DateTime::createFromFormat($this->format, $value);
+        return DateTime::createFromFormat($this->format, $value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return sprintf('Representation of date and time in "%s" format', $this->format);
     }
diff --git a/src/Type/Scalar/DateTimeTzType.php b/src/Type/Scalar/DateTimeTzType.php
index bdec1154..00d4929e 100644
--- a/src/Type/Scalar/DateTimeTzType.php
+++ b/src/Type/Scalar/DateTimeTzType.php
@@ -8,45 +8,49 @@
 
 namespace Youshido\GraphQL\Type\Scalar;
 
+use DateTime;
+use DateTimeInterface;
+
 class DateTimeTzType extends AbstractScalarType
 {
-    private $format = 'D, d M Y H:i:s O';
+    private string $format = 'D, d M Y H:i:s O';
 
-    public function getName()
+    public function getName(): string
     {
         return 'DateTimeTz';
     }
-    public function isValidValue($value)
+
+    public function isValidValue(mixed $value): bool
     {
-        if ((is_object($value) && $value instanceof \DateTimeInterface) || is_null($value)) {
+        if (($value instanceof DateTimeInterface) || is_null($value)) {
             return true;
-        } else if (is_string($value)) {
+        } elseif (is_string($value)) {
             $date = $this->createFromFormat($value);
         } else {
             $date = null;
         }
 
-        return $date ? true : false;
+        return (bool)$date;
     }
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         $date = null;
 
         if (is_string($value)) {
             $date = $this->createFromFormat($value);
-        } elseif ($value instanceof \DateTimeInterface) {
+        } elseif ($value instanceof DateTimeInterface) {
             $date = $value;
         }
 
         return $date ? $date->format($this->format) : null;
     }
 
-    public function parseValue($value)
+    public function parseValue($value): bool|null|DateTimeInterface|DateTime
     {
         if (is_string($value)) {
             $date = $this->createFromFormat($value);
-        } elseif ($value instanceof \DateTimeInterface) {
+        } elseif ($value instanceof DateTimeInterface) {
             $date = $value;
         } else {
             $date = false;
@@ -55,12 +59,12 @@ public function parseValue($value)
         return $date ?: null;
     }
 
-    private function createFromFormat($value)
+    private function createFromFormat(string $value): DateTime|bool
     {
-        return \DateTime::createFromFormat($this->format, $value);
+        return DateTime::createFromFormat($this->format, $value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'Representation of date and time in "r" format';
     }
diff --git a/src/Type/Scalar/DateType.php b/src/Type/Scalar/DateType.php
index b37c92a5..c42dfe74 100644
--- a/src/Type/Scalar/DateType.php
+++ b/src/Type/Scalar/DateType.php
@@ -8,45 +8,27 @@
 
 namespace Youshido\GraphQL\Type\Scalar;
 
+use DateTime;
+
 /**
  * @deprecated USE DateTime type instead. To be removed in 1.4.
  *
  * Class DateType
  * @package Youshido\GraphQL\Type\Scalar
  */
-class DateType extends AbstractScalarType
+class DateType extends DateTimeType
 {
-
-    public function getName()
-    {
-        return 'Date';
-    }
-
-    /**
-     * @param $value \DateTime
-     * @return null|string
-     */
-    public function serialize($value)
+    public function __construct()
     {
-        if ($value === null) {
-            return null;
-        }
-
-        return $value->format('Y-m-d');
+        parent::__construct('Y-m-d');
     }
 
-    public function isValidValue($value)
+    public function getName(): string
     {
-        if (is_null($value) || is_object($value)) {
-            return true;
-        }
-
-        $d = \DateTime::createFromFormat('Y-m-d', $value);
-
-        return $d && $d->format('Y-m-d') == $value;
+        return 'Date';
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'DEPRECATED. Use DateTime instead';
     }
diff --git a/src/Type/Scalar/FloatType.php b/src/Type/Scalar/FloatType.php
index 8aa99919..b143a7ec 100644
--- a/src/Type/Scalar/FloatType.php
+++ b/src/Type/Scalar/FloatType.php
@@ -11,30 +11,29 @@
 class FloatType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'Float';
     }
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         if ($value === null) {
             return null;
         } else {
-            return floatval($value);
+            return (float)$value;
         }
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_null($value) || is_float($value) || is_int($value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
-        return 'The `Float` scalar type represents signed double-precision fractional ' .
-               'values as specified by ' .
-               '[IEEE 754](http://en.wikipedia.org/wiki/IEEE_floating_point).';
+        return 'The `Float` scalar type represents signed double-precision fractional values as specified by ' .
+            '[IEEE 754](http://en.wikipedia.org/wiki/IEEE_floating_point).';
     }
 
 }
diff --git a/src/Type/Scalar/IdType.php b/src/Type/Scalar/IdType.php
index 07e3418c..03713732 100644
--- a/src/Type/Scalar/IdType.php
+++ b/src/Type/Scalar/IdType.php
@@ -12,12 +12,12 @@
 class IdType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'ID';
     }
 
-    public function serialize($value)
+    public function serialize($value): ?string
     {
         if (null === $value) {
             return null;
@@ -26,12 +26,12 @@ public function serialize($value)
         return (string)$value;
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'The `ID` scalar type represents a unique identifier, often used to ' .
-               'refetch an object or as key for a cache. The ID type appears in a JSON ' .
-               'response as a String; however, it is not intended to be human-readable. ' .
-               'When expected as an input type, any string (such as `"4"`) or integer ' .
-               '(such as `4`) input value will be accepted as an ID.';
+            'refetch an object or as key for a cache. The ID type appears in a JSON ' .
+            'response as a String; however, it is not intended to be human-readable. ' .
+            'When expected as an input type, any string (such as `"4"`) or integer ' .
+            '(such as `4`) input value will be accepted as an ID.';
     }
 }
diff --git a/src/Type/Scalar/IntType.php b/src/Type/Scalar/IntType.php
index b46d8aea..2cdd5e61 100644
--- a/src/Type/Scalar/IntType.php
+++ b/src/Type/Scalar/IntType.php
@@ -12,37 +12,35 @@
 class IntType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'Int';
     }
 
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         if ($value === null) {
             return null;
+        } elseif (is_int($value)) {
+            return $value;
         } else {
-            if (is_int($value)) {
-                return $value;
-            } else {
-                $value = (int)$value;
+            $value = (int)$value;
 
-                return $value != 0 ? $value : null;
-            }
+            return $value !== 0 ? $value : null;
         }
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_null($value) || is_int($value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'The `Int` scalar type represents non-fractional signed whole numeric ' .
-               'values. Int can represent values between -(2^53 - 1) and 2^53 - 1 since ' .
-               'represented in JSON as double-precision floating point numbers specified' .
-               'by [IEEE 754](http://en.wikipedia.org/wiki/IEEE_floating_point).';
+            'values. Int can represent values between -(2^53 - 1) and 2^53 - 1 since ' .
+            'represented in JSON as double-precision floating point numbers specified' .
+            'by [IEEE 754](http://en.wikipedia.org/wiki/IEEE_floating_point).';
     }
 
 }
diff --git a/src/Type/Scalar/StringType.php b/src/Type/Scalar/StringType.php
index 56390511..c7a345ec 100644
--- a/src/Type/Scalar/StringType.php
+++ b/src/Type/Scalar/StringType.php
@@ -12,12 +12,12 @@
 class StringType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'String';
     }
 
-    public function serialize($value)
+    public function serialize($value): ?string
     {
         if ($value === true) {
             return 'true';
@@ -27,23 +27,23 @@ public function serialize($value)
             return null;
         }
 
-        if(is_array($value)) {
+        if (is_array($value)) {
             return '';
         }
 
-        return (string) $value;
+        return (string)$value;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return is_null($value) || is_scalar($value) || ((is_object($value) && method_exists($value, '__toString')));
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'The `String` scalar type represents textual data, represented as UTF-8 ' .
-               'character sequences. The String type is most often used by GraphQL to ' .
-               'represent free-form human-readable text.';
+            'character sequences. The String type is most often used by GraphQL to ' .
+            'represent free-form human-readable text.';
     }
 
 }
diff --git a/src/Type/Scalar/TimestampType.php b/src/Type/Scalar/TimestampType.php
index 295745f4..b490e358 100644
--- a/src/Type/Scalar/TimestampType.php
+++ b/src/Type/Scalar/TimestampType.php
@@ -9,6 +9,8 @@
 namespace Youshido\GraphQL\Type\Scalar;
 
 
+use DateTime;
+
 /**
  * Class TimestampType
  * @package Youshido\GraphQL\Type\Scalar
@@ -17,16 +19,16 @@
 class TimestampType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'Timestamp';
     }
 
     /**
-     * @param $value \DateTime
+     * @param $value DateTime
      * @return null|string
      */
-    public function serialize($value)
+    public function serialize($value): mixed
     {
         if ($value === null || !is_object($value)) {
             return null;
@@ -35,7 +37,7 @@ public function serialize($value)
         return $value->getTimestamp();
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         if (is_null($value) || is_object($value)) {
             return true;
@@ -44,7 +46,7 @@ public function isValidValue($value)
         return is_int($value);
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'DEPRECATED. Will be converted to a real timestamp';
     }
diff --git a/src/Type/SchemaDirectivesList.php b/src/Type/SchemaDirectivesList.php
index c79c0bd1..5562c889 100644
--- a/src/Type/SchemaDirectivesList.php
+++ b/src/Type/SchemaDirectivesList.php
@@ -9,23 +9,17 @@
 
 use Youshido\GraphQL\Directive\DirectiveInterface;
 
-
 class SchemaDirectivesList
 {
-
-    private $directivesList = [];
+    private array $directivesList = [];
 
     /**
-     * @param array $directives
      *
-     * @throws
      * @return $this
+     * @throws
      */
-    public function addDirectives($directives)
+    public function addDirectives(array $directives): static
     {
-        if (!is_array($directives)) {
-            throw new \Exception('addDirectives accept only array of directives');
-        }
         foreach ($directives as $directive) {
             $this->addDirective($directive);
         }
@@ -34,35 +28,31 @@ public function addDirectives($directives)
     }
 
     /**
-     * @param DirectiveInterface $directive
-     *
      * @return $this
      */
-    public function addDirective(DirectiveInterface $directive)
+    public function addDirective(DirectiveInterface $directive): static
     {
         $directiveName = $this->getDirectiveName($directive);
-        if ($this->isDirectiveNameRegistered($directiveName)) return $this;
+        if ($this->isDirectiveNameRegistered($directiveName)) {
+            return $this;
+        }
 
         $this->directivesList[$directiveName] = $directive;
 
         return $this;
     }
 
-    private function getDirectiveName($directive)
+    private function getDirectiveName(DirectiveInterface $directive): string
     {
-        if (is_string($directive)) return $directive;
-        if (is_object($directive) && $directive instanceof DirectiveInterface) {
-            return $directive->getName();
-        }
-        throw new \Exception('Invalid directive passed to Schema');
+        return $directive->getName();
     }
 
-    public function isDirectiveNameRegistered($directiveName)
+    public function isDirectiveNameRegistered($directiveName): bool
     {
         return (isset($this->directivesList[$directiveName]));
     }
 
-    public function getDirectives()
+    public function getDirectives(): array
     {
         return $this->directivesList;
     }
diff --git a/src/Type/SchemaTypesList.php b/src/Type/SchemaTypesList.php
index 2c957edc..69986d3b 100644
--- a/src/Type/SchemaTypesList.php
+++ b/src/Type/SchemaTypesList.php
@@ -9,56 +9,62 @@
 namespace Youshido\GraphQL\Type;
 
 
+use Exception;
+
 class SchemaTypesList
 {
 
-    private $typesList = [];
+    private array $typesList = [];
 
     /**
-     * @param array $types
-     * @throws
      * @return $this
+     * @throws
      */
-    public function addTypes($types)
+    public function addTypes(array $types): static
     {
-        if (!is_array($types)) {
-            throw new \Exception('addTypes accept only array of types');
-        }
-        foreach($types as $type) {
+        foreach ($types as $type) {
             $this->addType($type);
         }
+
         return $this;
     }
 
-    public function getTypes()
+    public function getTypes(): array
     {
         return $this->typesList;
     }
 
     /**
-     * @param TypeInterface $type
      * @return $this
+     * @throws Exception
      */
-    public function addType(TypeInterface $type)
+    public function addType(TypeInterface $type): static
     {
         $typeName = $this->getTypeName($type);
-        if ($this->isTypeNameRegistered($typeName)) return $this;
+        if ($this->isTypeNameRegistered($typeName)) {
+            return $this;
+        }
 
         $this->typesList[$typeName] = $type;
         return $this;
     }
 
-    public function isTypeNameRegistered($typeName)
+    public function isTypeNameRegistered($typeName): bool
     {
         return (isset($this->typesList[$typeName]));
     }
 
-    private function getTypeName($type) {
-        if (is_string($type)) return $type;
-        if (is_object($type) && $type instanceof AbstractType) {
+    /**
+     * @throws Exception
+     */
+    private function getTypeName(TypeInterface $type): ?string
+    {
+
+        if ($type instanceof AbstractType) {
             return $type->getName();
         }
-        throw new \Exception('Invalid type passed to Schema');
+
+        throw new Exception('Invalid type passed to Schema');
     }
 
 }
\ No newline at end of file
diff --git a/src/Type/Traits/ArgumentsAwareObjectTrait.php b/src/Type/Traits/ArgumentsAwareObjectTrait.php
index 1778690f..5469905d 100644
--- a/src/Type/Traits/ArgumentsAwareObjectTrait.php
+++ b/src/Type/Traits/ArgumentsAwareObjectTrait.php
@@ -9,7 +9,12 @@
 namespace Youshido\GraphQL\Type\Traits;
 
 
+use Youshido\GraphQL\Config\AbstractConfig;
+use Youshido\GraphQL\Config\Field\FieldConfig;
+use Youshido\GraphQL\Config\Field\InputFieldConfig;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Config\Traits\ConfigAwareTrait;
+use Youshido\GraphQL\Field\InputField;
 
 /**
  * Class ArgumentsAwareObjectTrait
@@ -22,32 +27,32 @@ trait ArgumentsAwareObjectTrait
 {
     use ConfigAwareTrait;
 
-    public function addArgument($argument, $argumentInfo = null)
+    public function addArgument($argument, $argumentInfo = null): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->getConfig()->addArgument($argument, $argumentInfo);
     }
 
-    public function removeArgument($argumentName)
+    public function removeArgument($argumentName): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->getConfig()->removeArgument($argumentName);
     }
 
-    public function getArguments()
+    public function getArguments(): array
     {
         return $this->getConfig()->getArguments();
     }
 
-    public function getArgument($argumentName)
+    public function getArgument(string $argumentName): ?InputField
     {
         return $this->getConfig()->getArgument($argumentName);
     }
 
-    public function hasArgument($argumentName)
+    public function hasArgument(string $argumentName): bool
     {
         return $this->getConfig()->hasArgument($argumentName);
     }
 
-    public function hasArguments()
+    public function hasArguments(): bool
     {
         return $this->getConfig()->hasArguments();
     }
diff --git a/src/Type/Traits/AutoNameTrait.php b/src/Type/Traits/AutoNameTrait.php
index 6c27416b..8facef5d 100644
--- a/src/Type/Traits/AutoNameTrait.php
+++ b/src/Type/Traits/AutoNameTrait.php
@@ -7,6 +7,7 @@
 */
 
 namespace Youshido\GraphQL\Type\Traits;
+
 use Youshido\GraphQL\Field\FieldInterface;
 
 /**
@@ -15,10 +16,9 @@
  */
 trait AutoNameTrait
 {
-
-    public function getName()
+    public function getName(): ?string
     {
-        if (!empty($this->config)) {
+        if (!empty($this->config?->getName())) {
             return $this->config->getName();
         }
 
@@ -27,9 +27,10 @@ public function getName()
         if ($prevPos = strrpos($className, '\\')) {
             $className = substr($className, $prevPos + 1);
         }
-        if (substr($className, -5) == 'Field') {
+
+        if (str_ends_with($className, 'Field')) {
             $className = lcfirst(substr($className, 0, -5));
-        } elseif (substr($className, -4) == 'Type') {
+        } elseif (str_ends_with($className, 'Type')) {
             $className = substr($className, 0, -4);
         }
 
@@ -37,8 +38,6 @@ public function getName()
             $className = lcfirst($className);
         }
 
-
         return $className;
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Type/Traits/FieldsArgumentsAwareObjectTrait.php b/src/Type/Traits/FieldsArgumentsAwareObjectTrait.php
index 0a613a60..9ffd3b1e 100644
--- a/src/Type/Traits/FieldsArgumentsAwareObjectTrait.php
+++ b/src/Type/Traits/FieldsArgumentsAwareObjectTrait.php
@@ -9,44 +9,51 @@
 namespace Youshido\GraphQL\Type\Traits;
 
 
+use Youshido\GraphQL\Config\AbstractConfig;
+use Youshido\GraphQL\Config\Field\FieldConfig;
+use Youshido\GraphQL\Config\Field\InputFieldConfig;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Field\InputField;
+use Youshido\GraphQL\Parser\Ast\Argument;
+
 trait FieldsArgumentsAwareObjectTrait
 {
     use FieldsAwareObjectTrait;
 
-    protected $hasArgumentCache = null;
+    protected bool $hasArgumentCache = false;
 
-    public function addArguments($argumentsList)
+    public function addArguments($argumentsList): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->getConfig()->addArguments($argumentsList);
     }
 
-    public function removeArgument($argumentName)
+    public function removeArgument($argumentName): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->getConfig()->removeArgument($argumentName);
     }
 
-    public function addArgument($argument, $ArgumentInfo = null)
+    public function addArgument($argument, $ArgumentInfo = null): AbstractConfig|ObjectTypeConfig|FieldConfig|InputFieldConfig
     {
         return $this->getConfig()->addArgument($argument, $ArgumentInfo);
     }
 
-    public function getArguments()
+    public function getArguments(): array
     {
         return $this->getConfig()->getArguments();
     }
 
-    public function getArgument($argumentName)
+    public function getArgument(string $argumentName): InputField
     {
         return $this->getConfig()->getArgument($argumentName);
     }
 
-    public function hasArgument($argumentName)
+    public function hasArgument(string $argumentName): bool
     {
         return $this->getConfig()->hasArgument($argumentName);
     }
 
-    public function hasArguments()
+    public function hasArguments(): bool
     {
-        return $this->hasArgumentCache === null ? ($this->hasArgumentCache = $this->getConfig()->hasArguments()) : $this->hasArgumentCache;
+        return empty($this->hasArgumentCache) ? ($this->hasArgumentCache = $this->getConfig()->hasArguments()) : $this->hasArgumentCache;
     }
 }
diff --git a/src/Type/Traits/FieldsAwareObjectTrait.php b/src/Type/Traits/FieldsAwareObjectTrait.php
index e05ad69d..57d0b2cd 100644
--- a/src/Type/Traits/FieldsAwareObjectTrait.php
+++ b/src/Type/Traits/FieldsAwareObjectTrait.php
@@ -10,26 +10,33 @@
 
 
 use Youshido\GraphQL\Config\Traits\ConfigAwareTrait;
+use Youshido\GraphQL\Exception\ConfigurationException;
 
 trait FieldsAwareObjectTrait
 {
     use ConfigAwareTrait;
 
-    public function addFields($fieldsList)
+    /**
+     * @throws ConfigurationException
+     */
+    public function addFields($fieldsList): static
     {
         $this->getConfig()->addFields($fieldsList);
 
         return $this;
     }
 
-    public function addField($field, $fieldInfo = null)
+    /**
+     * @throws ConfigurationException
+     */
+    public function addField($field, $fieldInfo = null): static
     {
         $this->getConfig()->addField($field, $fieldInfo);
 
         return $this;
     }
 
-    public function getFields()
+    public function getFields(): array
     {
         return $this->getConfig()->getFields();
     }
@@ -39,14 +46,13 @@ public function getField($fieldName)
         return $this->getConfig()->getField($fieldName);
     }
 
-    public function hasField($fieldName)
+    public function hasField($fieldName): bool
     {
         return $this->getConfig()->hasField($fieldName);
     }
 
-    public function hasFields()
+    public function hasFields(): bool
     {
         return $this->getConfig()->hasFields();
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Type/TypeFactory.php b/src/Type/TypeFactory.php
index 25f2550b..b4f46aaf 100644
--- a/src/Type/TypeFactory.php
+++ b/src/Type/TypeFactory.php
@@ -8,33 +8,37 @@
 
 namespace Youshido\GraphQL\Type;
 
-
 use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
 
 class TypeFactory
 {
-    private static $objectsHash = [];
+    private static array $objectsHash = [];
 
     /**
-     * @param string $type
      *
      * @throws ConfigurationException
-     * @return AbstractScalarType
      */
-    public static function getScalarType($type)
+    public static function getScalarType(string $type): ?AbstractScalarType
     {
         if (TypeService::isScalarType($type)) {
-            if (is_object($type)) {
-                return $type;
-            }
             if (empty(self::$objectsHash[$type])) {
                 $name = ucfirst($type);
 
-                $name = $name == 'Datetime' ? 'DateTime' : $name;
-                $name = $name == 'Datetimetz' ? 'DateTimeTz' : $name;
+                $name = $name === 'Datetime' ? 'DateTime' : $name;
+                $name = $name === 'Datetimetz' ? 'DateTimeTz' : $name;
+
+                $className = 'Youshido\GraphQL\Type\Scalar\\' . $name . 'Type';
+
+                // Hotfix for our custom app - TODO - add via configuration
+                if (in_array($name, ['DateTimeAsString', 'StringOrArray', 'Boolean', 'Float', 'Int'])) {
+                    $className = 'App\GraphQL\Schema\Type\Scalar\\' . $name . 'Type';
+                    // Fallback to base scalar types if custom doesn't exist
+                    if (!class_exists($className)) {
+                        $className = 'Youshido\GraphQL\Type\Scalar\\' . $name . 'Type';
+                    }
+                }
 
-                $className                = 'Youshido\GraphQL\Type\Scalar\\' . $name . 'Type';
                 self::$objectsHash[$type] = new $className();
             }
 
@@ -47,7 +51,7 @@ public static function getScalarType($type)
     /**
      * @return string[]
      */
-    public static function getScalarTypesNames()
+    public static function getScalarTypesNames(): array
     {
         return [
             TypeMap::TYPE_INT,
@@ -59,6 +63,8 @@ public static function getScalarTypesNames()
             TypeMap::TYPE_DATE,
             TypeMap::TYPE_TIMESTAMP,
             TypeMap::TYPE_DATETIMETZ,
+            TypeMap::TYPE_DATETIME_AS_STRING,
+            TypeMap::TYPE_STRING_OR_ARRAY
         ];
     }
 }
diff --git a/src/Type/TypeInterface.php b/src/Type/TypeInterface.php
index 5688b32c..04740333 100644
--- a/src/Type/TypeInterface.php
+++ b/src/Type/TypeInterface.php
@@ -8,7 +8,7 @@
 
 namespace Youshido\GraphQL\Type;
 
-Interface TypeInterface extends InputTypeInterface
+interface TypeInterface extends InputTypeInterface
 {
 
 }
\ No newline at end of file
diff --git a/src/Type/TypeMap.php b/src/Type/TypeMap.php
index 336b2fbd..d622d190 100644
--- a/src/Type/TypeMap.php
+++ b/src/Type/TypeMap.php
@@ -10,25 +10,41 @@
 
 class TypeMap
 {
+    final const KIND_SCALAR = 'SCALAR';
 
-    const KIND_SCALAR       = 'SCALAR';
-    const KIND_OBJECT       = 'OBJECT';
-    const KIND_INTERFACE    = 'INTERFACE';
-    const KIND_UNION        = 'UNION';
-    const KIND_ENUM         = 'ENUM';
-    const KIND_INPUT_OBJECT = 'INPUT_OBJECT';
-    const KIND_LIST         = 'LIST';
-    const KIND_NON_NULL     = 'NON_NULL';
-
-    const TYPE_INT        = 'int';
-    const TYPE_FLOAT      = 'float';
-    const TYPE_STRING     = 'string';
-    const TYPE_BOOLEAN    = 'boolean';
-    const TYPE_ID         = 'id';
-    const TYPE_DATETIME   = 'datetime';
-    const TYPE_DATETIMETZ = 'datetimetz';
-    const TYPE_DATE       = 'date';
-    const TYPE_TIMESTAMP  = 'timestamp';
+    final const KIND_OBJECT = 'OBJECT';
 
+    final const KIND_INTERFACE = 'INTERFACE';
 
+    final const KIND_UNION = 'UNION';
+
+    final const KIND_ENUM = 'ENUM';
+
+    final const KIND_INPUT_OBJECT = 'INPUT_OBJECT';
+
+    final const KIND_LIST = 'LIST';
+
+    final const KIND_NON_NULL = 'NON_NULL';
+
+    final const TYPE_INT = 'int';
+
+    final const TYPE_FLOAT = 'float';
+
+    final const TYPE_STRING = 'string';
+
+    final const TYPE_BOOLEAN = 'boolean';
+
+    final const TYPE_ID = 'id';
+
+    final const TYPE_DATETIME = 'datetime';
+
+    final const TYPE_DATETIMETZ = 'datetimetz';
+
+    final const TYPE_DATETIME_AS_STRING = 'datetimeasstring';
+
+    final const TYPE_DATE = 'date';
+
+    final const TYPE_TIMESTAMP = 'timestamp';
+
+    final const TYPE_STRING_OR_ARRAY = 'stringorarray';
 }
diff --git a/src/Type/TypeService.php b/src/Type/TypeService.php
index cb1a29cf..9e89d1fe 100644
--- a/src/Type/TypeService.php
+++ b/src/Type/TypeService.php
@@ -9,6 +9,7 @@
 namespace Youshido\GraphQL\Type;
 
 
+use Exception;
 use Symfony\Component\PropertyAccess\PropertyAccess;
 use Youshido\GraphQL\Type\Enum\AbstractEnumType;
 use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
@@ -20,23 +21,41 @@
 class TypeService
 {
 
-    const TYPE_CALLABLE               = 'callable';
-    const TYPE_GRAPHQL_TYPE           = 'graphql_type';
-    const TYPE_OBJECT_TYPE            = 'object_type';
-    const TYPE_ARRAY_OF_OBJECT_TYPES  = 'array_of_object_types';
-    const TYPE_OBJECT_INPUT_TYPE      = 'object_input_type';
-    const TYPE_LIST                   = 'list';
-    const TYPE_BOOLEAN                = TypeMap::TYPE_BOOLEAN;
-    const TYPE_STRING                 = TypeMap::TYPE_STRING;
-    const TYPE_ARRAY                  = 'array';
-    const TYPE_ARRAY_OF_FIELDS_CONFIG = 'array_of_fields';
-    const TYPE_ARRAY_OF_INPUT_FIELDS  = 'array_of_inputs';
-    const TYPE_ENUM_VALUES            = 'array_of_values';
-    const TYPE_ARRAY_OF_INTERFACES    = 'array_of_interfaces';
-    const TYPE_ANY                    = 'any';
-    const TYPE_ANY_OBJECT             = 'any_object';
-    const TYPE_ANY_INPUT              = 'any_input';
+    final const TYPE_CALLABLE = 'callable';
 
+    final const TYPE_GRAPHQL_TYPE = 'graphql_type';
+
+    final const TYPE_OBJECT_TYPE = 'object_type';
+
+    final const TYPE_ARRAY_OF_OBJECT_TYPES = 'array_of_object_types';
+
+    final const TYPE_OBJECT_INPUT_TYPE = 'object_input_type';
+
+    final const TYPE_LIST = 'list';
+
+    final const TYPE_BOOLEAN = TypeMap::TYPE_BOOLEAN;
+
+    final const TYPE_STRING = TypeMap::TYPE_STRING;
+
+    final const TYPE_ARRAY = 'array';
+
+    final const TYPE_ARRAY_OF_FIELDS_CONFIG = 'array_of_fields';
+
+    final const TYPE_ARRAY_OF_INPUT_FIELDS = 'array_of_inputs';
+
+    final const TYPE_ENUM_VALUES = 'array_of_values';
+
+    final const TYPE_ARRAY_OF_INTERFACES = 'array_of_interfaces';
+
+    final const TYPE_ANY = 'any';
+
+    final const TYPE_ANY_OBJECT = 'any_object';
+
+    final const TYPE_ANY_INPUT = 'any_input';
+
+    /**
+     * @throws Exception
+     */
     public static function resolveNamedType($object)
     {
         if (is_object($object)) {
@@ -49,14 +68,13 @@ public static function resolveNamedType($object)
             return new StringType();
         }
 
-        throw new \Exception('Invalid type');
+        throw new Exception('Invalid type');
     }
 
     /**
      * @param AbstractType|mixed $type
-     * @return bool
      */
-    public static function isInterface($type)
+    public static function isInterface(mixed $type): bool
     {
         if (!is_object($type)) {
             return false;
@@ -67,9 +85,8 @@ public static function isInterface($type)
 
     /**
      * @param AbstractType|mixed $type
-     * @return bool
      */
-    public static function isAbstractType($type)
+    public static function isAbstractType(mixed $type): bool
     {
         if (!is_object($type)) {
             return false;
@@ -78,65 +95,62 @@ public static function isAbstractType($type)
         return in_array($type->getKind(), [TypeMap::KIND_INTERFACE, TypeMap::KIND_UNION]);
     }
 
-    public static function isScalarType($type)
+    public static function isScalarType($type): bool
     {
         if (is_object($type)) {
-            return $type instanceof AbstractScalarType || $type instanceof AbstractEnumType;
+            return $type instanceof AbstractScalarType;
         }
 
-        return in_array(strtolower($type), TypeFactory::getScalarTypesNames());
+        return in_array(strtolower((string)$type), TypeFactory::getScalarTypesNames());
     }
 
-    public static function isGraphQLType($type)
+    public static function isGraphQLType($type): bool
     {
         return $type instanceof AbstractType || TypeService::isScalarType($type);
     }
 
-    public static function isLeafType($type)
+    public static function isLeafType($type): bool
     {
         return $type instanceof AbstractEnumType || TypeService::isScalarType($type);
     }
 
-    public static function isObjectType($type)
+    public static function isObjectType($type): bool
     {
         return $type instanceof AbstractObjectType;
     }
 
     /**
      * @param mixed|AbstractType $type
-     * @return bool
      */
-    public static function isInputType($type)
+    public static function isInputType(mixed $type): bool
     {
         if (is_object($type)) {
             $namedType = $type->getNullableType()->getNamedType();
 
             return ($namedType instanceof AbstractScalarType)
-                   || ($type instanceof AbstractListType)
-                   || ($namedType instanceof AbstractInputObjectType)
-                   || ($namedType instanceof AbstractEnumType);
+                || ($type instanceof AbstractListType)
+                || ($namedType instanceof AbstractInputObjectType)
+                || ($namedType instanceof AbstractEnumType);
         } else {
             return TypeService::isScalarType($type);
         }
     }
 
-    public static function isInputObjectType($type)
+    public static function isInputObjectType($type): bool
     {
         return $type instanceof AbstractInputObjectType;
     }
 
     /**
-     * @param object|array $data
-     * @param string       $path
-     * @param bool         $enableMagicCall whether to attempt to resolve properties using __call()
+     * @param bool $enableMagicCall whether to attempt to resolve properties using __call()
      *
      * @return mixed|null
      */
-    public static function getPropertyValue($data, $path, $enableMagicCall = false)
+    public static function getPropertyValue(object|array $data, string $path, bool $enableMagicCall = false): mixed
     {
         // Normalize the path
         if (is_array($data)) {
-            $path = "[$path]";
+            $path = sprintf('[%s]', $path);
         }
 
         // Optionally enable __call() support
@@ -150,4 +164,4 @@ public static function getPropertyValue($data, $path, $enableMagicCall = false)
 
         return $propertyAccessor->isReadable($data, $path) ? $propertyAccessor->getValue($data, $path) : null;
     }
-}
+}
\ No newline at end of file
diff --git a/src/Type/Union/AbstractUnionType.php b/src/Type/Union/AbstractUnionType.php
index 1b3c3410..267811a8 100644
--- a/src/Type/Union/AbstractUnionType.php
+++ b/src/Type/Union/AbstractUnionType.php
@@ -11,8 +11,12 @@
 
 use Youshido\GraphQL\Config\Object\UnionTypeConfig;
 use Youshido\GraphQL\Config\Traits\ConfigAwareTrait;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Type\AbstractInterfaceTypeInterface;
 use Youshido\GraphQL\Type\AbstractType;
+use Youshido\GraphQL\Type\InputObject\AbstractInputObjectType;
+use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
+use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
 use Youshido\GraphQL\Type\Traits\AutoNameTrait;
@@ -21,18 +25,19 @@
 abstract class AbstractUnionType extends AbstractType implements AbstractInterfaceTypeInterface
 {
 
-    use ConfigAwareTrait, AutoNameTrait;
+    use ConfigAwareTrait;
+    use AutoNameTrait;
 
-    protected $isFinal = false;
+    protected bool $isFinal = false;
 
     /**
      * ObjectType constructor.
-     * @param $config
+     * @throws ConfigurationException
      */
-    public function __construct($config = [])
+    public function __construct(array $config = [])
     {
-        if (empty($config)) {
-            $config['name']  = $this->getName();
+        if ($config === []) {
+            $config['name'] = $this->getName();
             $config['types'] = $this->getTypes();
         }
 
@@ -42,19 +47,19 @@ public function __construct($config = [])
     /**
      * @return AbstractObjectType[]|AbstractScalarType[]
      */
-    abstract public function getTypes();
+    abstract public function getTypes(): array;
 
-    public function getKind()
+    public function getKind(): string
     {
         return TypeMap::KIND_UNION;
     }
 
-    public function getNamedType()
+    public function getNamedType(): AbstractUnionType|static
     {
         return $this;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         return true;
     }
diff --git a/src/Type/Union/UnionType.php b/src/Type/Union/UnionType.php
index f419159b..1e737cd0 100644
--- a/src/Type/Union/UnionType.php
+++ b/src/Type/Union/UnionType.php
@@ -8,19 +8,21 @@
 
 namespace Youshido\GraphQL\Type\Union;
 
+use Youshido\GraphQL\Type\AbstractType;
+
 final class UnionType extends AbstractUnionType
 {
 
-    protected $isFinal = true;
+    protected bool $isFinal = true;
 
-    public function resolveType($object)
+    public function resolveType(object $object): ?AbstractType
     {
         $callable = $this->getConfigValue('resolveType');
 
         return $callable($object);
     }
 
-    public function getTypes()
+    public function getTypes(): array
     {
         return $this->getConfig()->get('types', []);
     }
diff --git a/src/Validator/ConfigValidator/ConfigValidator.php b/src/Validator/ConfigValidator/ConfigValidator.php
index 9cd7957d..9454a08b 100644
--- a/src/Validator/ConfigValidator/ConfigValidator.php
+++ b/src/Validator/ConfigValidator/ConfigValidator.php
@@ -36,10 +36,7 @@ private function __construct()
         $this->initializeRules();
     }
 
-    /**
-     * @return ConfigValidator
-     */
-    public static function getInstance()
+    public static function getInstance(): ConfigValidator
     {
         if (empty(self::$instance)) {
             self::$instance = new self();
@@ -50,19 +47,22 @@ public static function getInstance()
         return self::$instance;
     }
 
-    public function assertValidConfig(AbstractConfig $config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function assertValidConfig(AbstractConfig $config): void
     {
         if (!$this->isValidConfig($config)) {
             throw new ConfigurationException('Config is not valid for ' . ($config->getContextObject() ? get_class($config->getContextObject()) : null) . "\n" . implode("\n", $this->getErrorsArray(false)));
         }
     }
 
-    public function isValidConfig(AbstractConfig $config)
+    public function isValidConfig(AbstractConfig $config): bool
     {
         return $this->validate($config->getData(), $this->getConfigFinalRules($config), $config->isExtraFieldsAllowed());
     }
 
-    protected function getConfigFinalRules(AbstractConfig $config)
+    protected function getConfigFinalRules(AbstractConfig $config): array
     {
         $rules = $config->getRules();
         if ($config->isFinalClass()) {
@@ -77,9 +77,11 @@ protected function getConfigFinalRules(AbstractConfig $config)
     }
 
 
-    public function validate($data, $rules = [], $extraFieldsAllowed = null)
+    public function validate($data, $rules = [], $extraFieldsAllowed = null): bool
     {
-        if ($extraFieldsAllowed !== null) $this->setExtraFieldsAllowed($extraFieldsAllowed);
+        if ($extraFieldsAllowed !== null) {
+            $this->setExtraFieldsAllowed($extraFieldsAllowed);
+        }
 
         $processedFields = [];
         foreach ($rules as $fieldName => $fieldRules) {
@@ -97,7 +99,10 @@ public function validate($data, $rules = [], $extraFieldsAllowed = null)
             } elseif (!array_key_exists($fieldName, $data)) {
                 continue;
             }
-            if (!empty($fieldRules['final'])) unset($fieldRules['final']);
+
+            if (!empty($fieldRules['final'])) {
+                unset($fieldRules['final']);
+            }
 
             /** Validation of all other rules*/
             foreach ($fieldRules as $ruleName => $ruleInfo) {
@@ -124,36 +129,31 @@ public function validate($data, $rules = [], $extraFieldsAllowed = null)
         return $this->isValid();
     }
 
-    protected function initializeRules()
+    protected function initializeRules(): void
     {
         $this->validationRules['type'] = new TypeValidationRule($this);
     }
 
-    public function addRule($name, ValidationRuleInterface $rule)
+    public function addRule($name, ValidationRuleInterface $rule): void
     {
         $this->validationRules[$name] = $rule;
     }
 
-    public function isValid()
+    public function isValid(): bool
     {
         return !$this->hasErrors();
     }
 
 
-    /**
-     * @return boolean
-     */
-    public function isExtraFieldsAllowed()
+    public function isExtraFieldsAllowed(): bool
     {
         return $this->extraFieldsAllowed;
     }
 
     /**
      * @param boolean $extraFieldsAllowed
-     *
-     * @return ConfigValidator
      */
-    public function setExtraFieldsAllowed($extraFieldsAllowed)
+    public function setExtraFieldsAllowed($extraFieldsAllowed): static
     {
         $this->extraFieldsAllowed = $extraFieldsAllowed;
 
diff --git a/src/Validator/ConfigValidator/ConfigValidatorInterface.php b/src/Validator/ConfigValidator/ConfigValidatorInterface.php
index 1b3d2adf..744f2204 100644
--- a/src/Validator/ConfigValidator/ConfigValidatorInterface.php
+++ b/src/Validator/ConfigValidator/ConfigValidatorInterface.php
@@ -11,6 +11,6 @@
 interface ConfigValidatorInterface
 {
 
-    public function validate($data, $rules = [], $allowExtraFields = null);
+    public function validate($data, $rules = [], $allowAllowAllowExtraFields = null);
 
 }
diff --git a/src/Validator/ConfigValidator/Rules/TypeValidationRule.php b/src/Validator/ConfigValidator/Rules/TypeValidationRule.php
index 1b068f61..1a53bf20 100644
--- a/src/Validator/ConfigValidator/Rules/TypeValidationRule.php
+++ b/src/Validator/ConfigValidator/Rules/TypeValidationRule.php
@@ -9,6 +9,7 @@
 namespace Youshido\GraphQL\Validator\ConfigValidator\Rules;
 
 
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\FieldInterface;
 use Youshido\GraphQL\Field\InputFieldInterface;
 use Youshido\GraphQL\Type\AbstractType;
@@ -18,72 +19,45 @@
 
 class TypeValidationRule implements ValidationRuleInterface
 {
-
-    private $configValidator;
+    private readonly ConfigValidator $configValidator;
 
     public function __construct(ConfigValidator $validator)
     {
         $this->configValidator = $validator;
     }
 
-    public function validate($data, $ruleInfo)
+    /**
+     * @throws ConfigurationException
+     */
+    public function validate($data, $ruleInfo): bool
     {
-        if (!is_string($ruleInfo)) return false;
-
-        switch ($ruleInfo) {
-            case TypeService::TYPE_ANY:
-                return true;
-
-            case TypeService::TYPE_ANY_OBJECT:
-                return is_object($data);
-
-            case TypeService::TYPE_CALLABLE:
-                return is_callable($data);
-
-            case TypeService::TYPE_BOOLEAN:
-                return is_bool($data);
-
-            case TypeService::TYPE_ARRAY:
-                return is_array($data);
-
-            case TypeService::TYPE_STRING:
-                return TypeFactory::getScalarType($ruleInfo)->isValidValue($data);
-
-            case TypeService::TYPE_GRAPHQL_TYPE:
-                return TypeService::isGraphQLType($data);
-
-            case TypeService::TYPE_OBJECT_TYPE:
-                return TypeService::isObjectType($data);
-
-            case TypeService::TYPE_ARRAY_OF_OBJECT_TYPES:
-                return $this->isArrayOfObjectTypes($data);
-
-            case TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG:
-                return $this->isArrayOfFields($data);
-
-            case TypeService::TYPE_OBJECT_INPUT_TYPE:
-                return TypeService::isInputObjectType($data);
-
-            case TypeService::TYPE_ENUM_VALUES:
-                return $this->isEnumValues($data);
-
-            case TypeService::TYPE_ARRAY_OF_INPUT_FIELDS:
-                return $this->isArrayOfInputFields($data);
-
-            case TypeService::TYPE_ANY_INPUT:
-                return TypeService::isInputType($data);
-
-            case TypeService::TYPE_ARRAY_OF_INTERFACES:
-                return $this->isArrayOfInterfaces($data);
-
-            default:
-                return false;
+        if (!is_string($ruleInfo)) {
+            return false;
         }
+
+        return match ($ruleInfo) {
+            TypeService::TYPE_ANY => true,
+            TypeService::TYPE_ANY_OBJECT => is_object($data),
+            TypeService::TYPE_CALLABLE => is_callable($data),
+            TypeService::TYPE_BOOLEAN => is_bool($data),
+            TypeService::TYPE_ARRAY => is_array($data),
+            TypeService::TYPE_STRING => TypeFactory::getScalarType($ruleInfo)->isValidValue($data),
+            TypeService::TYPE_GRAPHQL_TYPE => TypeService::isGraphQLType($data),
+            TypeService::TYPE_OBJECT_TYPE => TypeService::isObjectType($data),
+            TypeService::TYPE_ARRAY_OF_OBJECT_TYPES => $this->isArrayOfObjectTypes($data),
+            TypeService::TYPE_ARRAY_OF_FIELDS_CONFIG => $this->isArrayOfFields($data),
+            TypeService::TYPE_OBJECT_INPUT_TYPE => TypeService::isInputObjectType($data),
+            TypeService::TYPE_ENUM_VALUES => $this->isEnumValues($data),
+            TypeService::TYPE_ARRAY_OF_INPUT_FIELDS => $this->isArrayOfInputFields($data),
+            TypeService::TYPE_ANY_INPUT => TypeService::isInputType($data),
+            TypeService::TYPE_ARRAY_OF_INTERFACES => $this->isArrayOfInterfaces($data),
+            default => false,
+        };
     }
 
-    private function isArrayOfObjectTypes($data)
+    private function isArrayOfObjectTypes($data): bool
     {
-        if (!is_array($data) || !count($data)) {
+        if (!is_array($data) || $data === []) {
             return false;
         }
 
@@ -96,9 +70,11 @@ private function isArrayOfObjectTypes($data)
         return true;
     }
 
-    private function isEnumValues($data)
+    private function isEnumValues($data): bool
     {
-        if (!is_array($data) || empty($data)) return false;
+        if (!is_array($data) || $data === []) {
+            return false;
+        }
 
         foreach ($data as $item) {
             if (!is_array($item) || !array_key_exists('name', $item) || !is_string($item['name']) || !preg_match('/^[_a-zA-Z][_a-zA-Z0-9]*$/', $item['name'])) {
@@ -113,9 +89,11 @@ private function isEnumValues($data)
         return true;
     }
 
-    private static function isArrayOfInterfaces($data)
+    private function isArrayOfInterfaces($data): bool
     {
-        if (!is_array($data)) return false;
+        if (!is_array($data)) {
+            return false;
+        }
 
         foreach ($data as $item) {
             if (!TypeService::isInterface($item)) {
@@ -126,18 +104,22 @@ private static function isArrayOfInterfaces($data)
         return true;
     }
 
-    private function isArrayOfFields($data)
+    private function isArrayOfFields($data): bool
     {
-        if (!is_array($data) || empty($data)) return false;
+        if (!is_array($data) || $data === []) {
+            return false;
+        }
 
         foreach ($data as $name => $item) {
-            if (!$this->isField($item, $name)) return false;
+            if (!$this->isField($item, $name)) {
+                return false;
+            }
         }
 
         return true;
     }
 
-    private function isField($data, $name = null)
+    private function isField($data, $name = null): bool
     {
         if (is_object($data)) {
             if (($data instanceof FieldInterface) || ($data instanceof AbstractType)) {
@@ -146,6 +128,7 @@ private function isField($data, $name = null)
                 return false;
             }
         }
+
         if (!is_array($data)) {
             $data = [
                 'type' => $data,
@@ -154,23 +137,28 @@ private function isField($data, $name = null)
         } elseif (empty($data['name'])) {
             $data['name'] = $name;
         }
+
         $this->configValidator->validate($data, $this->getFieldConfigRules());
 
         return $this->configValidator->isValid();
     }
 
-    private function isArrayOfInputFields($data)
+    private function isArrayOfInputFields($data): bool
     {
-        if (!is_array($data)) return false;
+        if (!is_array($data)) {
+            return false;
+        }
 
-        foreach ($data as $name => $item) {
-            if (!$this->isInputField($item)) return false;
+        foreach ($data as $item) {
+            if (!$this->isInputField($item)) {
+                return false;
+            }
         }
 
         return true;
     }
 
-    private function isInputField($data)
+    private function isInputField(array $data): bool
     {
         if (is_object($data)) {
             if ($data instanceof InputFieldInterface) {
@@ -189,20 +177,18 @@ private function isInputField($data)
 
     /**
      * Exists for the performance
-     * @return array
      */
-    private function getFieldConfigRules()
+    private function getFieldConfigRules(): array
     {
         return [
-            'name'              => ['type' => TypeService::TYPE_STRING, 'required' => true],
-            'type'              => ['type' => TypeService::TYPE_ANY, 'required' => true],
-            'args'              => ['type' => TypeService::TYPE_ARRAY],
-            'description'       => ['type' => TypeService::TYPE_STRING],
-            'resolve'           => ['type' => TypeService::TYPE_CALLABLE],
-            'isDeprecated'      => ['type' => TypeService::TYPE_BOOLEAN],
+            'name' => ['type' => TypeService::TYPE_STRING, 'required' => true],
+            'type' => ['type' => TypeService::TYPE_ANY, 'required' => true],
+            'args' => ['type' => TypeService::TYPE_ARRAY],
+            'description' => ['type' => TypeService::TYPE_STRING],
+            'resolve' => ['type' => TypeService::TYPE_CALLABLE],
+            'isDeprecated' => ['type' => TypeService::TYPE_BOOLEAN],
             'deprecationReason' => ['type' => TypeService::TYPE_STRING],
-            'cost'              => ['type' => TypeService::TYPE_ANY]
+            'cost' => ['type' => TypeService::TYPE_ANY]
         ];
     }
-
-}
+}
\ No newline at end of file
diff --git a/src/Validator/ErrorContainer/ErrorContainerInterface.php b/src/Validator/ErrorContainer/ErrorContainerInterface.php
index 7da1dc8f..ec9d8087 100644
--- a/src/Validator/ErrorContainer/ErrorContainerInterface.php
+++ b/src/Validator/ErrorContainer/ErrorContainerInterface.php
@@ -8,15 +8,19 @@
 namespace Youshido\GraphQL\Validator\ErrorContainer;
 
 
+use Exception;
+
 interface ErrorContainerInterface
 {
 
-    public function addError(\Exception $exception);
+    public function addError(Exception $exception);
 
     public function mergeErrors(ErrorContainerInterface $errorContainer);
 
     public function hasErrors();
 
+    public function hasError(Exception $exception);
+
     public function getErrors();
 
     public function getErrorsArray();
diff --git a/src/Validator/ErrorContainer/ErrorContainerTrait.php b/src/Validator/ErrorContainer/ErrorContainerTrait.php
index 93bc3b22..3d17647a 100644
--- a/src/Validator/ErrorContainer/ErrorContainerTrait.php
+++ b/src/Validator/ErrorContainer/ErrorContainerTrait.php
@@ -7,33 +7,40 @@
 
 namespace Youshido\GraphQL\Validator\ErrorContainer;
 
+use Exception;
 use Youshido\GraphQL\Exception\Interfaces\ExtendedExceptionInterface;
 use Youshido\GraphQL\Exception\Interfaces\LocationableExceptionInterface;
 
 trait ErrorContainerTrait
 {
+    /** @var Exception[] */
+    protected array $errors = [];
 
-    /** @var \Exception[] */
-    protected $errors = [];
-
-    public function addError(\Exception $exception)
+    public function addError(Exception $exception): static
     {
-        $this->errors[] = $exception;
+        if (!$this->hasError($exception)) {
+            $this->errors[] = $exception;
+        }
 
         return $this;
     }
 
-    public function hasErrors()
+    public function hasErrors(): bool
+    {
+        return !empty($this->errors);
+    }
+
+    public function hasError(Exception $exception): bool
     {
-        return ! empty($this->errors);
+        return $this->hasErrors() && in_array($exception, $this->errors);
     }
 
-    public function getErrors()
+    public function getErrors(): array
     {
         return $this->errors;
     }
 
-    public function mergeErrors(ErrorContainerInterface $errorContainer)
+    public function mergeErrors(ErrorContainerInterface $errorContainer): static
     {
         if ($errorContainer->hasErrors()) {
             foreach ($errorContainer->getErrors() as $error) {
@@ -44,7 +51,7 @@ public function mergeErrors(ErrorContainerInterface $errorContainer)
         return $this;
     }
 
-    public function getErrorsArray($inGraphQLStyle = true)
+    public function getErrorsArray(bool $inGraphQLStyle = true): array
     {
         $errors = [];
 
@@ -79,11 +86,10 @@ public function getErrorsArray($inGraphQLStyle = true)
         return $errors;
     }
 
-    public function clearErrors()
+    public function clearErrors(): static
     {
         $this->errors = [];
 
         return $this;
     }
-
 }
diff --git a/src/Validator/RequestValidator/RequestValidator.php b/src/Validator/RequestValidator/RequestValidator.php
index 457afb28..26c2a40c 100644
--- a/src/Validator/RequestValidator/RequestValidator.php
+++ b/src/Validator/RequestValidator/RequestValidator.php
@@ -10,11 +10,15 @@
 
 use Youshido\GraphQL\Exception\Parser\InvalidRequestException;
 use Youshido\GraphQL\Execution\Request;
+use Youshido\GraphQL\Parser\Ast\Fragment;
 
 class RequestValidator implements RequestValidatorInterface
 {
 
-    public function validate(Request $request)
+    /**
+     * @throws InvalidRequestException
+     */
+    public function validate(Request $request): void
     {
         $this->assertFragmentReferencesValid($request);
         $this->assetFragmentsUsed($request);
@@ -22,7 +26,10 @@ public function validate(Request $request)
         $this->assertAllVariablesUsed($request);
     }
 
-    private function assetFragmentsUsed(Request $request)
+    /**
+     * @throws InvalidRequestException
+     */
+    private function assetFragmentsUsed(Request $request): void
     {
         foreach ($request->getFragmentReferences() as $fragmentReference) {
             $request->getFragment($fragmentReference->getName())->setUsed(true);
@@ -35,16 +42,22 @@ private function assetFragmentsUsed(Request $request)
         }
     }
 
-    private function assertFragmentReferencesValid(Request $request)
+    /**
+     * @throws InvalidRequestException
+     */
+    private function assertFragmentReferencesValid(Request $request): void
     {
         foreach ($request->getFragmentReferences() as $fragmentReference) {
-            if (!$request->getFragment($fragmentReference->getName())) {
+            if (!$request->getFragment($fragmentReference->getName()) instanceof Fragment) {
                 throw new InvalidRequestException(sprintf('Fragment "%s" not defined in query', $fragmentReference->getName()), $fragmentReference->getLocation());
             }
         }
     }
 
-    private function assertAllVariablesExists(Request $request)
+    /**
+     * @throws InvalidRequestException
+     */
+    private function assertAllVariablesExists(Request $request): void
     {
         foreach ($request->getVariableReferences() as $variableReference) {
             if (!$variableReference->getVariable()) {
@@ -53,7 +66,10 @@ private function assertAllVariablesExists(Request $request)
         }
     }
 
-    private function assertAllVariablesUsed(Request $request)
+    /**
+     * @throws InvalidRequestException
+     */
+    private function assertAllVariablesUsed(Request $request): void
     {
         foreach ($request->getQueryVariables() as $queryVariable) {
             if (!$queryVariable->isUsed()) {
diff --git a/src/Validator/ResolveValidator/ResolveValidator.php b/src/Validator/ResolveValidator/ResolveValidator.php
index ab7e3963..9c2aa6c4 100644
--- a/src/Validator/ResolveValidator/ResolveValidator.php
+++ b/src/Validator/ResolveValidator/ResolveValidator.php
@@ -24,38 +24,41 @@
 class ResolveValidator implements ResolveValidatorInterface
 {
 
-    /** @var ExecutionContext */
-    private $executionContext;
+    private readonly ExecutionContext $executionContext;
 
 
     /**
      * ResolveValidator constructor.
-     *
-     * @param ExecutionContext $executionContext
      */
     public function __construct(ExecutionContext $executionContext)
     {
         $this->executionContext = $executionContext;
     }
-    
-    public function assetTypeHasField(AbstractType $objectType, AstFieldInterface $ast)
+
+    /**
+     * @throws ResolveException
+     */
+    public function assetTypeHasField(AbstractType $objectType, AstFieldInterface $ast): void
     {
         /** @var AbstractObjectType $objectType */
         if ($this->executionContext->getField($objectType, $ast->getName()) !== null) {
             return;
         }
-        
-        if (!(TypeService::isObjectType($objectType) || TypeService::isInputObjectType($objectType)) || !$objectType->hasField($ast->getName())) {
-            $availableFieldNames = implode(', ', array_map(function (FieldInterface $field) {
+
+        if (!TypeService::isObjectType($objectType) && !TypeService::isInputObjectType($objectType) || !$objectType->hasField($ast->getName())) {
+            $availableFieldNames = implode(', ', array_map(static function (FieldInterface $field): string {
                 return sprintf('"%s"', $field->getName());
             }, $objectType->getFields()));
             throw new ResolveException(sprintf('Field "%s" not found in type "%s". Available fields are: %s', $ast->getName(), $objectType->getNamedType()->getName(), $availableFieldNames), $ast->getLocation());
         }
     }
 
-    public function assertValidArguments(FieldInterface $field, AstFieldInterface $query, Request $request)
+    /**
+     * @throws ResolveException
+     */
+    public function assertValidArguments(FieldInterface $field, AstFieldInterface $query, Request $request): void
     {
-        $requiredArguments = array_filter($field->getArguments(), function (InputField $argument) {
+        $requiredArguments = array_filter($field->getArguments(), static function (InputField $argument): bool {
             return $argument->getType()->getKind() === TypeMap::KIND_NON_NULL;
         });
 
@@ -64,7 +67,7 @@ public function assertValidArguments(FieldInterface $field, AstFieldInterface $q
                 throw new ResolveException(sprintf('Unknown argument "%s" on field "%s"', $astArgument->getName(), $field->getName()), $astArgument->getLocation());
             }
 
-            $argument     = $field->getArgument($astArgument->getName());
+            $argument = $field->getArgument($astArgument->getName());
             $argumentType = $argument->getType()->getNullableType();
 
             switch ($argumentType->getKind()) {
@@ -88,12 +91,15 @@ public function assertValidArguments(FieldInterface $field, AstFieldInterface $q
             }
         }
 
-        if (count($requiredArguments)) {
+        if ($requiredArguments !== []) {
             throw new ResolveException(sprintf('Require "%s" arguments to query "%s"', implode(', ', array_keys($requiredArguments)), $query->getName()));
         }
     }
 
-    public function assertValidResolvedValueForField(FieldInterface $field, $resolvedValue)
+    /**
+     * @throws ResolveException
+     */
+    public function assertValidResolvedValueForField(FieldInterface $field, $resolvedValue): void
     {
         if (null === $resolvedValue && $field->getType()->getKind() === TypeMap::KIND_NON_NULL) {
             throw new ResolveException(sprintf('Cannot return null for non-nullable field "%s"', $field->getName()));
@@ -107,7 +113,10 @@ public function assertValidResolvedValueForField(FieldInterface $field, $resolve
         }
     }
 
-    public function assertTypeImplementsInterface(AbstractType $type, AbstractInterfaceType $interface)
+    /**
+     * @throws ResolveException
+     */
+    public function assertTypeImplementsInterface(AbstractType $type, AbstractInterfaceType $interface): void
     {
         if ($type instanceof AbstractObjectType) {
             foreach ($type->getInterfaces() as $typeInterface) {
@@ -120,7 +129,10 @@ public function assertTypeImplementsInterface(AbstractType $type, AbstractInterf
         throw new ResolveException(sprintf('Type "%s" does not implement "%s"', $type->getName(), $interface->getName()));
     }
 
-    public function assertTypeInUnionTypes(AbstractType $type, AbstractUnionType $unionType)
+    /**
+     * @throws ResolveException
+     */
+    public function assertTypeInUnionTypes(AbstractType $type, AbstractUnionType $unionType): void
     {
         foreach ($unionType->getTypes() as $unionTypeItem) {
             if ($unionTypeItem->getName() === $type->getName()) {
diff --git a/src/Validator/SchemaValidator/SchemaValidator.php b/src/Validator/SchemaValidator/SchemaValidator.php
index 78365e22..0b334c5a 100644
--- a/src/Validator/SchemaValidator/SchemaValidator.php
+++ b/src/Validator/SchemaValidator/SchemaValidator.php
@@ -18,23 +18,19 @@
 class SchemaValidator
 {
 
-    /** @var ConfigValidator */
-    private $configValidator = null;
     /**
-     * @param AbstractSchema $schema
-     *
      * @throws ConfigurationException
      */
-    public function validate(AbstractSchema $schema)
+    public function validate(AbstractSchema $schema): void
     {
         if (!$schema->getQueryType()->hasFields()) {
             throw new ConfigurationException('Schema has to have fields');
         }
 
-        $this->configValidator = ConfigValidator::getInstance();
+        $configValidator = ConfigValidator::getInstance();
 
         foreach ($schema->getQueryType()->getConfig()->getFields() as $field) {
-            $this->configValidator->assertValidConfig($field->getConfig());
+            $configValidator->assertValidConfig($field->getConfig());
 
             if ($field->getType() instanceof AbstractObjectType) {
                 $this->assertInterfaceImplementationCorrect($field->getType());
@@ -43,11 +39,9 @@ public function validate(AbstractSchema $schema)
     }
 
     /**
-     * @param AbstractObjectType $type
-     *
      * @throws ConfigurationException
      */
-    protected function assertInterfaceImplementationCorrect(AbstractObjectType $type)
+    protected function assertInterfaceImplementationCorrect(AbstractObjectType $type): void
     {
         if (!$type->getInterfaces()) {
             return;
@@ -61,18 +55,18 @@ protected function assertInterfaceImplementationCorrect(AbstractObjectType $type
     }
 
     /**
-     * @param Field                 $intField
-     * @param Field                 $objField
-     * @param AbstractInterfaceType $interface
+     * @param Field $intField
+     * @param Field $objField
      *
      * @throws ConfigurationException
      */
-    protected function assertFieldsIdentical($intField, $objField, AbstractInterfaceType $interface)
+    protected function assertFieldsIdentical($intField, $objField, AbstractInterfaceType $interface): void
     {
         $isValid = true;
         if ($intField->getType()->isCompositeType() !== $objField->getType()->isCompositeType()) {
             $isValid = false;
         }
+
         if ($intField->getType()->getNamedType()->getName() != $objField->getType()->getNamedType()->getName()) {
             $isValid = false;
         }
diff --git a/tests/DataProvider/TestConfig.php b/tests/DataProvider/TestConfig.php
index 802baae6..2a669dcb 100644
--- a/tests/DataProvider/TestConfig.php
+++ b/tests/DataProvider/TestConfig.php
@@ -14,7 +14,7 @@
 
 class TestConfig extends AbstractConfig
 {
-    public function getRules()
+    public function getRules(): array
     {
         return [
             'name'    => ['type' => TypeService::TYPE_ANY, 'required' => true],
diff --git a/tests/DataProvider/TestConfigExtraFields.php b/tests/DataProvider/TestConfigExtraFields.php
index f8aa17e6..9f28992a 100644
--- a/tests/DataProvider/TestConfigExtraFields.php
+++ b/tests/DataProvider/TestConfigExtraFields.php
@@ -17,7 +17,7 @@ class TestConfigExtraFields extends AbstractConfig
 
     protected $extraFieldsAllowed = true;
 
-    public function getRules()
+    public function getRules(): array
     {
         return [
             'name' => ['type' => TypeService::TYPE_ANY, 'required' => true]
diff --git a/tests/DataProvider/TestConfigInvalidRule.php b/tests/DataProvider/TestConfigInvalidRule.php
index 0a61ab85..e7e31bb7 100644
--- a/tests/DataProvider/TestConfigInvalidRule.php
+++ b/tests/DataProvider/TestConfigInvalidRule.php
@@ -8,7 +8,7 @@
 
 class TestConfigInvalidRule extends AbstractConfig
 {
-    public function getRules()
+    public function getRules(): array
     {
         return [
             'name'             => ['type' => TypeService::TYPE_ANY, 'required' => true],
diff --git a/tests/DataProvider/TestEmptySchema.php b/tests/DataProvider/TestEmptySchema.php
index 004bc45e..b3d3b060 100644
--- a/tests/DataProvider/TestEmptySchema.php
+++ b/tests/DataProvider/TestEmptySchema.php
@@ -14,12 +14,12 @@
 
 class TestEmptySchema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
     }
 
 
-    public function getName($config)
+    public function getName($config): string
     {
         return 'TestSchema';
     }
diff --git a/tests/DataProvider/TestEnumType.php b/tests/DataProvider/TestEnumType.php
index 90a1b8d8..fdc60f2a 100644
--- a/tests/DataProvider/TestEnumType.php
+++ b/tests/DataProvider/TestEnumType.php
@@ -13,7 +13,7 @@
 
 class TestEnumType extends AbstractEnumType
 {
-    public function getValues()
+    public function getValues(): array
     {
         return [
             [
diff --git a/tests/DataProvider/TestExtendedType.php b/tests/DataProvider/TestExtendedType.php
index 4acc4252..2d1ea185 100644
--- a/tests/DataProvider/TestExtendedType.php
+++ b/tests/DataProvider/TestExtendedType.php
@@ -15,7 +15,7 @@
 
 class TestExtendedType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->applyInterface(new TestInterfaceType())
             ->addField('ownField', new StringType());
diff --git a/tests/DataProvider/TestField.php b/tests/DataProvider/TestField.php
index b1764754..53c94d2f 100644
--- a/tests/DataProvider/TestField.php
+++ b/tests/DataProvider/TestField.php
@@ -18,7 +18,7 @@ class TestField extends AbstractField
     /**
      * @return AbstractObjectType
      */
-    public function getType()
+    public function getType(): \Youshido\GraphQL\Type\Scalar\IntType
     {
         return new IntType();
     }
@@ -28,7 +28,7 @@ public function resolve($value, array $args, ResolveInfo $info)
         return $value;
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'description';
     }
diff --git a/tests/DataProvider/TestInputField.php b/tests/DataProvider/TestInputField.php
index 2340e560..20b165ed 100644
--- a/tests/DataProvider/TestInputField.php
+++ b/tests/DataProvider/TestInputField.php
@@ -18,17 +18,17 @@ class TestInputField extends AbstractInputField
     /**
      * @return InputTypeInterface
      */
-    public function getType()
+    public function getType(): \Youshido\GraphQL\Type\Scalar\IntType
     {
         return new IntType();
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'description';
     }
 
-    public function getDefaultValue()
+    public function getDefaultValue(): string
     {
         return 'default';
     }
diff --git a/tests/DataProvider/TestInputObjectType.php b/tests/DataProvider/TestInputObjectType.php
index 95d34b0a..fcbb063c 100644
--- a/tests/DataProvider/TestInputObjectType.php
+++ b/tests/DataProvider/TestInputObjectType.php
@@ -15,7 +15,7 @@
 
 class TestInputObjectType extends AbstractInputObjectType
 {
-    public function build($config)
+    public function build($config): void
     {
         $config->addField('name', new NonNullType(new StringType()));
     }
diff --git a/tests/DataProvider/TestInterfaceType.php b/tests/DataProvider/TestInterfaceType.php
index 68a562ad..489914d3 100644
--- a/tests/DataProvider/TestInterfaceType.php
+++ b/tests/DataProvider/TestInterfaceType.php
@@ -9,18 +9,19 @@
 namespace Youshido\Tests\DataProvider;
 
 
+use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
 use Youshido\GraphQL\Type\Scalar\StringType;
 
 class TestInterfaceType extends AbstractInterfaceType
 {
 
-    public function resolveType($object)
+    public function resolveType($object): object
     {
         return is_object($object) ? $object : new TestObjectType();
     }
 
-    public function build($config)
+    public function build(InterfaceTypeConfig $config): void
     {
         $config->addField('name', new StringType());
     }
diff --git a/tests/DataProvider/TestListType.php b/tests/DataProvider/TestListType.php
index 87f779c4..22c9bee3 100644
--- a/tests/DataProvider/TestListType.php
+++ b/tests/DataProvider/TestListType.php
@@ -14,7 +14,7 @@
 
 class TestListType extends AbstractListType
 {
-    public function getItemType()
+    public function getItemType(): \Youshido\GraphQL\Type\Scalar\StringType
     {
         return new StringType();
     }
diff --git a/tests/DataProvider/TestMutationObjectType.php b/tests/DataProvider/TestMutationObjectType.php
index c0747499..62a03a47 100644
--- a/tests/DataProvider/TestMutationObjectType.php
+++ b/tests/DataProvider/TestMutationObjectType.php
@@ -9,18 +9,19 @@
 namespace Youshido\Tests\DataProvider;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\Object\AbstractMutationObjectType;
 use Youshido\GraphQL\Type\Scalar\IntType;
 use Youshido\GraphQL\Type\Scalar\StringType;
 
 class TestMutationObjectType extends AbstractMutationObjectType
 {
-    public function getOutputType()
+    public function getOutputType(): \Youshido\GraphQL\Type\Scalar\StringType
     {
         return new StringType();
     }
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $this->addArgument('increment', new IntType());
     }
diff --git a/tests/DataProvider/TestObjectType.php b/tests/DataProvider/TestObjectType.php
index f0e43a8b..638a0909 100644
--- a/tests/DataProvider/TestObjectType.php
+++ b/tests/DataProvider/TestObjectType.php
@@ -8,6 +8,7 @@
 
 namespace Youshido\Tests\DataProvider;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Object\ObjectType;
 use Youshido\GraphQL\Type\Scalar\IntType;
@@ -17,7 +18,7 @@
 class TestObjectType extends AbstractObjectType
 {
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('id', new IntType())
@@ -41,8 +42,8 @@ public function build($config)
                  'args'    => [
                      'noop' => new IntType()
                  ],
-                 'resolve' => function ($value, $args, $info) {
-                   return ['address' => '1234 Street'];
+                 'resolve' => static function ($value, $args, $info) : array {
+                     return ['address' => '1234 Street'];
                  }
              ]
             )
@@ -52,19 +53,19 @@ public function build($config)
                     'args'    => [
                         'value' => new NonNullType(new StringType())
                     ],
-                    'resolve' => function ($value, $args, $info) {
+                    'resolve' => static function ($value, array $args, $info) {
                         return $args['value'];
                     }
                 ]
             );
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new TestInterfaceType()];
     }
 
-    public function getData()
+    public function getData(): array
     {
         return [
             'id'   => 1,
diff --git a/tests/DataProvider/TestResolveInfo.php b/tests/DataProvider/TestResolveInfo.php
index 2bf68c1c..6589f9d2 100644
--- a/tests/DataProvider/TestResolveInfo.php
+++ b/tests/DataProvider/TestResolveInfo.php
@@ -14,7 +14,7 @@
 
 class TestResolveInfo
 {
-    public static function createTestResolveInfo($field = null)
+    public static function createTestResolveInfo($field = null): \Youshido\GraphQL\Execution\ResolveInfo
     {
         if (empty($field)) {
             $field = new TestField();
diff --git a/tests/DataProvider/TestScalarDataProvider.php b/tests/DataProvider/TestScalarDataProvider.php
index b49a0771..5056e545 100644
--- a/tests/DataProvider/TestScalarDataProvider.php
+++ b/tests/DataProvider/TestScalarDataProvider.php
@@ -12,7 +12,7 @@ class TestScalarDataProvider
 {
 
 
-    public static function getsList()
+    public static function getsList(): array
     {
         return [
             "Int",
@@ -23,7 +23,7 @@ public static function getsList()
         ];
     }
 
-    public static function getIntTestData()
+    public static function getIntTestData(): array
     {
         /** input, serialization, isValid */
         return [
@@ -47,7 +47,7 @@ public static function getIntTestData()
         ];
     }
 
-    public static function getFloatTestData()
+    public static function getFloatTestData(): array
     {
         return [
             [1, 1.0, true],
@@ -63,7 +63,7 @@ public static function getFloatTestData()
         ];
     }
 
-    public static function getStringTestData()
+    public static function getStringTestData(): array
     {
         return [
             ["string", "string", true],
@@ -76,7 +76,7 @@ public static function getStringTestData()
         ];
     }
 
-    public static function getBooleanTestData()
+    public static function getBooleanTestData(): array
     {
         return [
             ["string", true, false],
@@ -92,7 +92,7 @@ public static function getBooleanTestData()
         ];
     }
 
-    public static function getIdTestData()
+    public static function getIdTestData(): array
     {
         return [
             ["string-id", "string-id", true],
@@ -101,7 +101,7 @@ public static function getIdTestData()
         ];
     }
 
-    public static function getDatetimeTestData()
+    public static function getDatetimeTestData(): array
     {
         $time = time();
         return [
@@ -110,7 +110,7 @@ public static function getDatetimeTestData()
         ];
     }
 
-    public static function getDatetimetzTestData()
+    public static function getDatetimetzTestData(): array
     {
         $time = time();
         return [
@@ -119,7 +119,7 @@ public static function getDatetimetzTestData()
         ];
     }
 
-    public static function getDateTestData()
+    public static function getDateTestData(): array
     {
         $time = time();
         return [
@@ -129,7 +129,7 @@ public static function getDateTestData()
     }
 
 
-    public static function getTimestampTestData()
+    public static function getTimestampTestData(): array
     {
         $time = time();
         return [
diff --git a/tests/DataProvider/TestSchema.php b/tests/DataProvider/TestSchema.php
index 26726d83..d3a32729 100644
--- a/tests/DataProvider/TestSchema.php
+++ b/tests/DataProvider/TestSchema.php
@@ -17,14 +17,14 @@
 
 class TestSchema extends AbstractSchema
 {
-    private $testStatusValue = 0;
+    private int $testStatusValue = 0;
 
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->getQuery()->addFields([
             'me'     => [
                 'type'    => new TestObjectType(),
-                'resolve' => function ($value, $args, ResolveInfo $info) {
+                'resolve' => static function ($value, $args, ResolveInfo $info) {
                     return $info->getReturnType()->getData();
                 }
             ],
diff --git a/tests/DataProvider/TestTimeType.php b/tests/DataProvider/TestTimeType.php
index 3d9f285b..fc59877b 100644
--- a/tests/DataProvider/TestTimeType.php
+++ b/tests/DataProvider/TestTimeType.php
@@ -9,41 +9,42 @@
 namespace Youshido\Tests\DataProvider;
 
 
+use DateTime;
 use Youshido\GraphQL\Type\Scalar\AbstractScalarType;
 
 class TestTimeType extends AbstractScalarType
 {
 
-    public function getName()
+    public function getName(): string
     {
         return 'TestTime';
     }
 
     /**
-     * @param $value \DateTime
-     * @return null|string
+     * @param $value DateTime
+     * @return string|DateTime|null
      */
-    public function serialize($value)
+    public function serialize($value): string|null|DateTime
     {
         if ($value === null) {
             return null;
         }
 
-        return $value instanceof \DateTime ? $value->format('H:i:s') : $value;
+        return $value instanceof DateTime ? $value->format('H:i:s') : $value;
     }
 
-    public function isValidValue($value)
+    public function isValidValue(mixed $value): bool
     {
         if (is_object($value)) {
             return true;
         }
 
-        $d = \DateTime::createFromFormat('H:i:s', $value);
+        $d = DateTime::createFromFormat('H:i:s', $value);
 
         return $d && $d->format('H:i:s') == $value;
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'Representation time in "H:i:s" format';
     }
diff --git a/tests/DataProvider/TestUnionType.php b/tests/DataProvider/TestUnionType.php
index 96e1dd9c..8738ea1f 100644
--- a/tests/DataProvider/TestUnionType.php
+++ b/tests/DataProvider/TestUnionType.php
@@ -13,19 +13,19 @@
 class TestUnionType extends AbstractUnionType
 {
 
-    public function getTypes()
+    public function getTypes(): array
     {
         return [
             new TestObjectType()
         ];
     }
 
-    public function resolveType($object)
+    public function resolveType(object $object)
     {
         return $object;
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'Union collect cars types';
     }
diff --git a/tests/Issues/Issue109/Issue109Schema.php b/tests/Issues/Issue109/Issue109Schema.php
index 8ba4ab8f..6535e13f 100644
--- a/tests/Issues/Issue109/Issue109Schema.php
+++ b/tests/Issues/Issue109/Issue109Schema.php
@@ -11,7 +11,7 @@
 class Issue109Schema extends AbstractSchema
 {
 
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->setQuery(
             new ObjectType([
@@ -40,14 +40,13 @@ public function build(SchemaConfig $config)
                                 ]
                             ]
                         ]),
-                        'resolve' => function ($source, array $args, ResolveInfo $info) {
+                        'resolve' => static function ($source, array $args, ResolveInfo $info) : array {
                             $internalArgs = [
                                 'comment_id' => 200
                             ];
                             if ($field = $info->getFieldAST('comments')->hasArguments()) {
                                 $internalArgs['comment_id'] = $info->getFieldAST('comments')->getArgumentValue('comment_id');
                             }
-
                             return [
                                 "id"       => 1,
                                 "title"    => "New approach in API has been revealed",
diff --git a/tests/Issues/Issue109/Issue109Test.php b/tests/Issues/Issue109/Issue109Test.php
index 0e6a9628..fe24765d 100644
--- a/tests/Issues/Issue109/Issue109Test.php
+++ b/tests/Issues/Issue109/Issue109Test.php
@@ -7,7 +7,7 @@
 class Issue109Test extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInternalVariableArgument()
+    public function testInternalVariableArgument(): void
     {
         $schema    = new Issue109Schema();
         $processor = new Processor($schema);
diff --git a/tests/Issues/Issue116/Issue116Test.php b/tests/Issues/Issue116/Issue116Test.php
index 3ad2ce71..4e31c0f9 100644
--- a/tests/Issues/Issue116/Issue116Test.php
+++ b/tests/Issues/Issue116/Issue116Test.php
@@ -13,7 +13,7 @@
 class Issue116Test extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInternalVariableArgument()
+    public function testInternalVariableArgument(): void
     {
         $schema    = new Schema([
             'query' => new ObjectType([
@@ -32,12 +32,11 @@ public function testInternalVariableArgument()
                                             'args'    => [
                                                 'size' => new NonNullType(new IntType()),
                                             ],
-                                            'resolve' => function ($source, $args) {
+                                            'resolve' => static function ($source, array $args) : array {
                                                 $res = [];
                                                 foreach (range(1, $args['size']) as $i) {
                                                     $res[] = 'Cursor #' . $i;
                                                 }
-
                                                 return $res;
                                             }
                                         ],
@@ -48,7 +47,7 @@ public function testInternalVariableArgument()
                         'args'    => [
                             'first' => new IntType(),
                         ],
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 'pageInfo' => [
                                     'totalEdges' => 10,
diff --git a/tests/Issues/Issue131/Issue131Test.php b/tests/Issues/Issue131/Issue131Test.php
index 1372dca1..2ac73fc4 100644
--- a/tests/Issues/Issue131/Issue131Test.php
+++ b/tests/Issues/Issue131/Issue131Test.php
@@ -15,7 +15,7 @@
 class Issue131Test extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInternalVariableArgument()
+    public function testInternalVariableArgument(): void
     {
 
 
@@ -47,7 +47,7 @@ public function testInternalVariableArgument()
                                 ]
                             ]))
                         ],
-                        'resolve' => function ($source, $args) {
+                        'resolve' => static function ($source, array $args) : array {
                             return [
                                 'id' => '1',
                                 'name' => sprintf('Meeting with %d beans', count($args['related_beans'])),
diff --git a/tests/Issues/Issue149/Issue149Test.php b/tests/Issues/Issue149/Issue149Test.php
index f42df1dc..956d3c16 100644
--- a/tests/Issues/Issue149/Issue149Test.php
+++ b/tests/Issues/Issue149/Issue149Test.php
@@ -13,7 +13,7 @@
 
 class Issue149Test extends \PHPUnit_Framework_TestCase
 {
-    public function testInternalVariableArgument()
+    public function testInternalVariableArgument(): void
     {
         $schema    = new Schema([
             'query' => new ObjectType([
@@ -36,7 +36,7 @@ public function testInternalVariableArgument()
                                 ])),
                             ],
                         ]),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 'id'      => 1,
                                 'name'    => 'John',
diff --git a/tests/Issues/Issue151/Issue151Test.php b/tests/Issues/Issue151/Issue151Test.php
index b3f58900..b1607637 100644
--- a/tests/Issues/Issue151/Issue151Test.php
+++ b/tests/Issues/Issue151/Issue151Test.php
@@ -12,7 +12,7 @@
 
 class Issue151Test extends \PHPUnit_Framework_TestCase
 {
-    public function testInternalVariableArgument()
+    public function testInternalVariableArgument(): void
     {
         $type1 = new ObjectType([
             'name'   => 'Type1',
@@ -32,11 +32,10 @@ public function testInternalVariableArgument()
         $unionType = new UnionType([
             'name'        => 'Union',
             'types'       => [$type1, $type2],
-            'resolveType' => function ($value) use ($type1, $type2) {
+            'resolveType' => static function (array $value) use ($type1, $type2) {
                 if (isset($value['name'])) {
                     return $type1;
                 }
-
                 return $type2;
             },
         ]);
@@ -47,7 +46,7 @@ public function testInternalVariableArgument()
                 'fields' => [
                     'list' => [
                         'type'    => new ListType($unionType),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 [
                                     'id'   => 1,
@@ -64,7 +63,7 @@ public function testInternalVariableArgument()
             ]),
         ]);
         $processor = new Processor($schema);
-        $response  = $processor->processPayload('
+        $processor->processPayload('
 {
     list {
         ...UnitFragment
diff --git a/tests/Issues/Issue171/Issue171Schema.php b/tests/Issues/Issue171/Issue171Schema.php
index 95110c24..d6a597b3 100644
--- a/tests/Issues/Issue171/Issue171Schema.php
+++ b/tests/Issues/Issue171/Issue171Schema.php
@@ -1,6 +1,7 @@
 <?php
 namespace Youshido\Tests\Issues\Issue171;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Config\Schema\SchemaConfig;
 use Youshido\GraphQL\Schema\AbstractSchema;
 use Youshido\GraphQL\Type\Enum\AbstractEnumType;
@@ -8,7 +9,7 @@
 
 class Issue171Schema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->getQuery()->addField(
             'plan',
@@ -21,7 +22,7 @@ public function build(SchemaConfig $config)
 
 class PlanType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addField('kpi_status', [
             'type' => new KpiStatusType(),
@@ -31,7 +32,7 @@ public function build($config)
 
 class KpiStatusType extends AbstractEnumType
 {
-    public function getValues()
+    public function getValues(): array
     {
         return [
             [
diff --git a/tests/Issues/Issue171/Issue171Test.php b/tests/Issues/Issue171/Issue171Test.php
index f4163bc6..12d1ff2e 100644
--- a/tests/Issues/Issue171/Issue171Test.php
+++ b/tests/Issues/Issue171/Issue171Test.php
@@ -5,15 +5,16 @@
 
 class Issue171Test extends \PHPUnit_Framework_TestCase
 {
-    public function testItSetsDeprecationReasonToNullByDefault()
+    public function testItSetsDeprecationReasonToNullByDefault(): void
     {
         $schema = new Issue171Schema();
         $processor = new Processor($schema);
 
         $processor->processPayload($this->getIntrospectionQuery(), []);
+        
         $resp = $processor->getResponseData();
 
-        $enumTypes = array_filter($resp['data']['__schema']['types'], function($type){
+        $enumTypes = array_filter($resp['data']['__schema']['types'], static function (array $type) : bool {
             return ($type['kind'] === 'ENUM');
         });
 
diff --git a/tests/Issues/Issue193/Issue193Test.php b/tests/Issues/Issue193/Issue193Test.php
index 80d673f0..a9565815 100644
--- a/tests/Issues/Issue193/Issue193Test.php
+++ b/tests/Issues/Issue193/Issue193Test.php
@@ -2,6 +2,8 @@
 
 namespace Youshido\Tests\Issues\Issue193;
 
+use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Config\Schema\SchemaConfig;
 use Youshido\GraphQL\Execution\Processor;
 use Youshido\GraphQL\Schema\AbstractSchema;
@@ -13,15 +15,16 @@
 
 class Issue193Test extends \PHPUnit_Framework_TestCase
 {
-    public function testResolvedInterfacesShouldBeRegistered()
+    public function testResolvedInterfacesShouldBeRegistered(): void
     {
         $schema    = new Issue193Schema();
         $processor = new Processor($schema);
 
         $processor->processPayload($this->getIntrospectionQuery(), []);
+        
         $resp = $processor->getResponseData();
 
-        $typeNames = array_map(function ($type) {
+        $typeNames = array_map(static function (array $type) {
             return $type['name'];
         }, $resp['data']['__schema']['types']);
 
@@ -67,7 +70,7 @@ private function getIntrospectionQuery()
 
 class Issue193Schema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->getQuery()->addField(
             'post',
@@ -81,7 +84,7 @@ public function build(SchemaConfig $config)
 class PostType extends AbstractObjectType
 {
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->applyInterface(new ContentBlockInterface());
         $config->addFields([
@@ -89,7 +92,7 @@ public function build($config)
         ]);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new ContentBlockInterface()];
     }
@@ -97,7 +100,7 @@ public function getInterfaces()
 
 class UndiscoveredType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->applyInterface(new ContentBlockInterface());
     }
@@ -105,13 +108,13 @@ public function build($config)
 
 class ContentBlockInterface extends AbstractInterfaceType
 {
-    public function build($config)
+    public function build(InterfaceTypeConfig $config): void
     {
         $config->addField('title', new NonNullType(new StringType()));
         $config->addField('summary', new StringType());
     }
 
-    public function resolveType($object)
+    public function resolveType($object): \Youshido\Tests\Issues\Issue193\PostType|\Youshido\Tests\Issues\Issue193\UndiscoveredType
     {
         if (isset($object['title'])) {
             return new PostType();
@@ -120,7 +123,7 @@ public function resolveType($object)
         return new UndiscoveredType();
     }
 
-    public function getImplementations()
+    public function getImplementations(): array
     {
         return [
             new PostType(),
diff --git a/tests/Issues/Issue194/ProcessorTest.php b/tests/Issues/Issue194/ProcessorTest.php
index 78a147cb..6d9b8d4b 100644
--- a/tests/Issues/Issue194/ProcessorTest.php
+++ b/tests/Issues/Issue194/ProcessorTest.php
@@ -13,7 +13,7 @@
 class ProcessorTest extends TestCase
 {
 
-    public function testNonNullDefaultValue()
+    public function testNonNullDefaultValue(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -27,7 +27,7 @@ public function testNonNullDefaultValue()
                                 'defaultValue' => 20,
                             ],
                         ],
-                        'resolve' => static function ($source, $args, ResolveInfo $info) {
+                        'resolve' => static function ($source, array $args, ResolveInfo $info): string {
                             return 'Alex age ' . $args['age'];
                         },
                     ],
@@ -44,7 +44,7 @@ public function testNonNullDefaultValue()
             $processor->processPayload('{ currentUser(age:10) }')->getResponseData());
     }
 
-    public function testNullDefaultValue()
+    public function testNullDefaultValue(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -58,7 +58,7 @@ public function testNullDefaultValue()
                                 'defaultValue' => null,
                             ],
                         ],
-                        'resolve' => static function ($source, $args, ResolveInfo $info) {
+                        'resolve' => static function ($source, array $args, ResolveInfo $info): string {
                             if ($args['age'] === null) {
                                 $args['age'] = 25;
                             }
diff --git a/tests/Issues/Issue201/Issue201Test.php b/tests/Issues/Issue201/Issue201Test.php
index b7810489..b2cf8acb 100644
--- a/tests/Issues/Issue201/Issue201Test.php
+++ b/tests/Issues/Issue201/Issue201Test.php
@@ -16,7 +16,7 @@ class Issue201Test extends TestCase
      * @expectedException \Youshido\GraphQL\Exception\ConfigurationException
      * @expectedExceptionMessage Type "user" was defined more than once
      */
-    public function testExceptionOnDuplicateTypeName()
+    public function testExceptionOnDuplicateTypeName(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
diff --git a/tests/Issues/Issue210/TypeServiceTest.php b/tests/Issues/Issue210/TypeServiceTest.php
index deca066d..200f4ef8 100644
--- a/tests/Issues/Issue210/TypeServiceTest.php
+++ b/tests/Issues/Issue210/TypeServiceTest.php
@@ -8,7 +8,7 @@
 class TypeServiceTest extends TestCase
 {
 
-    public function testGetPropertyValue()
+    public function testGetPropertyValue(): void
     {
         $object = new DummyObjectWithTrickyGetters();
 
@@ -20,17 +20,17 @@ public function testGetPropertyValue()
 
 class DummyObjectWithTrickyGetters
 {
-    public function getIssuer()
+    public function getIssuer(): string
     {
         return 'Foo';
     }
 
-    public function something()
+    public function something(): string
     {
         return 'something';
     }
 
-    public function issuerName()
+    public function issuerName(): string
     {
         return 'Bar';
     }
diff --git a/tests/Issues/Issue220/ResolvableObjectTraitTest.php b/tests/Issues/Issue220/ResolvableObjectTraitTest.php
index ae96b69c..10908a43 100644
--- a/tests/Issues/Issue220/ResolvableObjectTraitTest.php
+++ b/tests/Issues/Issue220/ResolvableObjectTraitTest.php
@@ -3,6 +3,7 @@
 namespace Youshido\Tests\Issues\Issue220;
 
 use PHPUnit\Framework\TestCase;
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Field\Field;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\StringType;
@@ -11,7 +12,7 @@
 class Issue220Test extends TestCase
 {
 
-    public function testValueNotFoundInResolveScalarType()
+    public function testValueNotFoundInResolveScalarType(): void
     {
         $fieldWithResolve = new Field([
             'name' => 'scalarField',
@@ -23,7 +24,7 @@ public function testValueNotFoundInResolveScalarType()
         $this->assertEquals(null, $fieldWithResolve->resolve([], [], $resolveInfo));
     }
 
-    public function testValueNotFoundInResolveObjectType()
+    public function testValueNotFoundInResolveObjectType(): void
     {
         $fieldWithResolve = new Field([
             'name' => 'scalarField',
@@ -35,7 +36,7 @@ public function testValueNotFoundInResolveObjectType()
         $this->assertEquals(null, $fieldWithResolve->resolve([], [], $resolveInfo));
     }
 
-    public function testValueFoundInResolve()
+    public function testValueFoundInResolve(): void
     {
         $fieldWithResolve = new Field([
             'name' => 'scalarField',
@@ -50,7 +51,7 @@ public function testValueFoundInResolve()
 
 class ArticleType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addFields([
             'title' => new StringType(),
diff --git a/tests/Issues/Issue90/Issue90Schema.php b/tests/Issues/Issue90/Issue90Schema.php
index 03f0d28a..ef77ddfe 100644
--- a/tests/Issues/Issue90/Issue90Schema.php
+++ b/tests/Issues/Issue90/Issue90Schema.php
@@ -9,7 +9,7 @@
 class Issue90Schema extends AbstractSchema
 {
 
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->setQuery(
             new ObjectType([
@@ -20,12 +20,10 @@ public function build(SchemaConfig $config)
                         'args'    => [
                             'date' => new DateTimeType('Y-m-d H:ia')
                         ],
-                        'resolve' => function ($value, $args, $info) {
-
+                        'resolve' => static function ($value, array $args, $info) {
                             if (isset($args['date'])) {
                                 return $args['date'];
                             }
-
                             return null;
                         }
                     ]
@@ -42,12 +40,10 @@ public function build(SchemaConfig $config)
                         'args'    => [
                             'date' => new DateTimeType('Y-m-d H:ia')
                         ],
-                        'resolve' => function ($value, $args, $info) {
-
+                        'resolve' => static function ($value, array $args, $info) {
                             if (isset($args['date'])) {
                                 return $args['date'];
                             }
-
                             return null;
                         }
                     ]
diff --git a/tests/Issues/Issue90/Issue90Test.php b/tests/Issues/Issue90/Issue90Test.php
index e30b2729..20720a6c 100644
--- a/tests/Issues/Issue90/Issue90Test.php
+++ b/tests/Issues/Issue90/Issue90Test.php
@@ -13,11 +13,12 @@
 class Issue90Test extends \PHPUnit_Framework_TestCase
 {
 
-    public function testQueryDateTimeTypeWithDateParameter()
+    public function testQueryDateTimeTypeWithDateParameter(): void
     {
         $schema = new Issue90Schema();
         $processor = new Processor($schema);
-        $processor->processPayload("query{ echo(date: \"2016-11-25 09:53am\") }");
+        $processor->processPayload('query{ echo(date: "2016-11-25 09:53am") }');
+        
         $res = $processor->getResponseData();
 
         self::assertCount(1, $res, "Invalid response array received"); //only data expected
@@ -27,10 +28,11 @@ public function testQueryDateTimeTypeWithDateParameter()
         self::assertEquals("2016-11-25 09:53am", $res['data']['echo']);
     }
 
-    public function testQueryDateTimeTypeWithoutParameter()
+    public function testQueryDateTimeTypeWithoutParameter(): void
     {
         $processor = new Processor(new Issue90Schema());
         $processor->processPayload("query{ echo }");
+        
         $res = $processor->getResponseData();
 
         self::assertCount(1, $res, "Invalid response array received"); //only data expected
@@ -38,10 +40,11 @@ public function testQueryDateTimeTypeWithoutParameter()
         self::assertNull($res['data']['echo']);
     }
 
-    public function testQueryDateTimeTypeWithNullParameter()
+    public function testQueryDateTimeTypeWithNullParameter(): void
     {
         $processor = new Processor(new Issue90Schema());
         $processor->processPayload("query{ echo(date: null) }");
+        
         $res = $processor->getResponseData();
 
         self::assertCount(1, $res, "Invalid response array received"); //only data expected
@@ -49,11 +52,12 @@ public function testQueryDateTimeTypeWithNullParameter()
         self::assertNull($res['data']['echo'], "Error Quering with explicit date null parameter ");
     }
 
-    public function testMutatingDateTimeWithParameter()
+    public function testMutatingDateTimeWithParameter(): void
     {
         $schema = new Issue90Schema();
         $processor = new Processor($schema);
-        $processor->processPayload("mutation{ echo(date: \"2016-11-25 09:53am\") }");
+        $processor->processPayload('mutation{ echo(date: "2016-11-25 09:53am") }');
+        
         $res = $processor->getResponseData();
 
         self::assertCount(1, $res, "Invalid response array received"); //only data expected
@@ -63,11 +67,12 @@ public function testMutatingDateTimeWithParameter()
         self::assertEquals("2016-11-25 09:53am", $res['data']['echo']);
     }
 
-    public function testMutatingDateTimeWithExplicitNullParameter()
+    public function testMutatingDateTimeWithExplicitNullParameter(): void
     {
         $schema = new Issue90Schema();
         $processor = new Processor($schema);
         $processor->processPayload("mutation{ echo(date: null) }");
+        
         $res = $processor->getResponseData();
 
         self::assertCount(1, $res, "Invalid response array received"); //only data expected
diff --git a/tests/Issues/Issue98/TypeServiceTest.php b/tests/Issues/Issue98/TypeServiceTest.php
index c137dea5..065d3cb5 100644
--- a/tests/Issues/Issue98/TypeServiceTest.php
+++ b/tests/Issues/Issue98/TypeServiceTest.php
@@ -7,7 +7,7 @@
 
 class TypeServiceTest extends TestCase
 {
-    public function testPropertGetValueWithMagicGet()
+    public function testPropertGetValueWithMagicGet(): void
     {
         $object = new DummyObjectWithMagicGet();
 
@@ -15,7 +15,7 @@ public function testPropertGetValueWithMagicGet()
         $this->assertEquals('getbar', TypeService::getPropertyValue($object, 'anything'));
     }
 
-    public function testPropertyGetValueWithMagicCall()
+    public function testPropertyGetValueWithMagicCall(): void
     {
         $object = new DummyObjectWithMagicCall();
 
diff --git a/tests/Issues/Issue99/Issue99Schema.php b/tests/Issues/Issue99/Issue99Schema.php
index 8ac032df..5620db80 100644
--- a/tests/Issues/Issue99/Issue99Schema.php
+++ b/tests/Issues/Issue99/Issue99Schema.php
@@ -13,7 +13,7 @@
 
 class Issue99Schema extends AbstractSchema
 {
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->setQuery(
             new ObjectType([
@@ -39,9 +39,8 @@ public function build(SchemaConfig $config)
                                             ]))
                                         ]
                                     ],
-                                    'resolve' => function($source, $args) {
+                                    'resolve' => static function ($source, array $args) : array {
                                         $x = isset($args['argX']['x']) ? $args['argX']['x'] : Issue99Test::BUG_EXISTS_VALUE;
-
                                         return [
                                             'value' => $x
                                         ];
@@ -52,7 +51,7 @@ public function build(SchemaConfig $config)
                         'args'    => [
                             'example' => new StringType()
                         ],
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 ['id' => 1],
                                 ['id' => 2],
diff --git a/tests/Issues/Issue99/Issue99Test.php b/tests/Issues/Issue99/Issue99Test.php
index ae6ebf5a..59df05e9 100644
--- a/tests/Issues/Issue99/Issue99Test.php
+++ b/tests/Issues/Issue99/Issue99Test.php
@@ -10,14 +10,16 @@
  */
 class Issue99Test extends \PHPUnit_Framework_TestCase
 {
-    const BUG_NOT_EXISTS_VALUE = 'bug not exists';
-    const BUG_EXISTS_VALUE = 'bug exists';
+    final const BUG_NOT_EXISTS_VALUE = 'bug not exists';
+    
+    final const BUG_EXISTS_VALUE = 'bug exists';
 
-    public function testQueryDateTimeTypeWithDateParameter()
+    public function testQueryDateTimeTypeWithDateParameter(): void
     {
         $schema = new Issue99Schema();
         $processor = new Processor($schema);
-        $processor->processPayload(sprintf("{ items{id, custom(argX: {x: \"%s\"}){ value } } }", self::BUG_NOT_EXISTS_VALUE));
+        $processor->processPayload(sprintf('{ items{id, custom(argX: {x: "%s"}){ value } } }', self::BUG_NOT_EXISTS_VALUE));
+        
         $res = $processor->getResponseData();
 
         self::assertTrue(isset($res['data']['items']));
diff --git a/tests/Library/Config/ConfigTest.php b/tests/Library/Config/ConfigTest.php
index 1fba5740..7607f9a4 100644
--- a/tests/Library/Config/ConfigTest.php
+++ b/tests/Library/Config/ConfigTest.php
@@ -24,7 +24,7 @@ class ConfigTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testEmptyParams()
+    public function testEmptyParams(): void
     {
         new TestConfig([]);
     }
@@ -32,7 +32,7 @@ public function testEmptyParams()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidParams()
+    public function testInvalidParams(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(new TestConfig(['id' => 1]));
     }
@@ -40,13 +40,13 @@ public function testInvalidParams()
     /**
      * @expectedException \Exception
      */
-    public function testInvalidMethod()
+    public function testInvalidMethod(): void
     {
         $config = new TestConfig(['name' => 'test']);
         $config->doSomethingStrange();
     }
 
-    public function testMethods()
+    public function testMethods(): void
     {
         $name  = 'Test';
         $rules = [
@@ -80,7 +80,9 @@ public function testMethods()
             ]
         ]);
 
-        $finalConfig = new TestConfig(['name' => $name . 'final', 'resolve' => function () { return []; }], $object, true);
+        $finalConfig = new TestConfig(['name' => $name . 'final', 'resolve' => static function () : array {
+            return [];
+        }], $object, true);
         $this->assertEquals($finalConfig->getType(), null);
 
         $rules['resolve']['required'] = true;
@@ -98,15 +100,15 @@ public function testMethods()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testFinalRule()
+    public function testFinalRule(): void
     {
-        ConfigValidator::getInstance()->assertValidConfig(new TestConfig(['name' => 'Test' . 'final'], null, true));
+        ConfigValidator::getInstance()->assertValidConfig(new TestConfig(['name' => 'Testfinal'], null, true));
     }
 
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidRule()
+    public function testInvalidRule(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(
             new TestConfigInvalidRule(['name' => 'Test', 'invalidRuleField' => 'test'], null, null)
@@ -116,7 +118,7 @@ public function testInvalidRule()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testEnumConfig()
+    public function testEnumConfig(): void
     {
         $enumType = new EnumType([
             'name'   => 'Status',
diff --git a/tests/Library/Config/FieldConfigTest.php b/tests/Library/Config/FieldConfigTest.php
index 4d14b8fd..bf860282 100644
--- a/tests/Library/Config/FieldConfigTest.php
+++ b/tests/Library/Config/FieldConfigTest.php
@@ -15,12 +15,12 @@
 class FieldConfigTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInvalidParams()
+    public function testInvalidParams(): void
     {
         $fieldConfig = new FieldConfig([
             'name'    => 'FirstName',
             'type'    => new StringType(),
-            'resolve' => function ($value, $args = [], $type = null) {
+            'resolve' => static function ($value, $args = [], $type = null) : string {
                 return 'John';
             }
         ]);
diff --git a/tests/Library/Config/InterfaceTypeConfigTest.php b/tests/Library/Config/InterfaceTypeConfigTest.php
index e462bec6..40f3fa32 100644
--- a/tests/Library/Config/InterfaceTypeConfigTest.php
+++ b/tests/Library/Config/InterfaceTypeConfigTest.php
@@ -19,7 +19,7 @@
 class InterfaceTypeConfigTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testCreation()
+    public function testCreation(): void
     {
         $config = new InterfaceTypeConfig(['name' => 'Test'], null, false);
         $this->assertEquals($config->getName(), 'Test', 'Normal creation');
@@ -28,17 +28,18 @@ public function testCreation()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testConfigNoFields()
+    public function testConfigNoFields(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(
-            new InterfaceTypeConfig(['name' => 'Test', 'resolveType' => function () { }], null, true)
+            new InterfaceTypeConfig(['name' => 'Test', 'resolveType' => static function () : void {
+            }], null, true)
         );
     }
 
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testConfigNoResolve()
+    public function testConfigNoResolve(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(
             new InterfaceTypeConfig(['name' => 'Test', 'fields' => ['id' => new IntType()]], null, true)
@@ -48,18 +49,18 @@ public function testConfigNoResolve()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testConfigInvalidResolve()
+    public function testConfigInvalidResolve(): void
     {
         $config = new InterfaceTypeConfig(['name' => 'Test', 'fields' => ['id' => new IntType()]], null, false);
         $config->resolveType(['invalid object']);
     }
 
-    public function testInterfaces()
+    public function testInterfaces(): void
     {
         $interfaceConfig = new InterfaceTypeConfig([
             'name'        => 'Test',
             'fields'      => ['id' => new IntType()],
-            'resolveType' => function ($object) {
+            'resolveType' => static function ($object) {
                 return $object->getType();
             }
         ], null, true);
diff --git a/tests/Library/Config/ObjectTypeConfigTest.php b/tests/Library/Config/ObjectTypeConfigTest.php
index 11819dc6..05daa426 100644
--- a/tests/Library/Config/ObjectTypeConfigTest.php
+++ b/tests/Library/Config/ObjectTypeConfigTest.php
@@ -16,7 +16,7 @@
 class ObjectTypeConfigTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testCreation()
+    public function testCreation(): void
     {
         $config = new ObjectTypeConfig(['name' => 'Test'], null, false);
         $this->assertEquals($config->getName(), 'Test', 'Normal creation');
@@ -25,7 +25,7 @@ public function testCreation()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidConfigNoFields()
+    public function testInvalidConfigNoFields(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(
             new ObjectTypeConfig(['name' => 'Test'], null, true)
@@ -35,14 +35,14 @@ public function testInvalidConfigNoFields()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidConfigInvalidInterface()
+    public function testInvalidConfigInvalidInterface(): void
     {
         ConfigValidator::getInstance()->assertValidConfig(
             new ObjectTypeConfig(['name' => 'Test', 'interfaces' => ['Invalid interface']], null, false)
         );
     }
 
-    public function testInterfaces()
+    public function testInterfaces(): void
     {
         $testInterfaceType = new TestInterfaceType();
         $config            = new ObjectTypeConfig(['name' => 'Test', 'interfaces' => [$testInterfaceType]], null, false);
diff --git a/tests/Library/Field/ArgumentsAwareConfigTraitTest.php b/tests/Library/Field/ArgumentsAwareConfigTraitTest.php
index e6250dea..55ee7658 100644
--- a/tests/Library/Field/ArgumentsAwareConfigTraitTest.php
+++ b/tests/Library/Field/ArgumentsAwareConfigTraitTest.php
@@ -17,7 +17,7 @@
 class ArgumentsAwareConfigTraitTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testArguments()
+    public function testArguments(): void
     {
         $argsData = [
             'id' => new IntType()
diff --git a/tests/Library/Field/FieldAwareConfigTraitTest.php b/tests/Library/Field/FieldAwareConfigTraitTest.php
index 50676020..08a61a66 100644
--- a/tests/Library/Field/FieldAwareConfigTraitTest.php
+++ b/tests/Library/Field/FieldAwareConfigTraitTest.php
@@ -17,7 +17,7 @@
 class FieldAwareConfigTraitTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testAddField()
+    public function testAddField(): void
     {
         $fieldsData = [
             'id' => [
@@ -32,6 +32,7 @@ public function testAddField()
         $this->assertTrue($config->hasFields());
         $idField = new Field(['name' => 'id', 'type' => new IntType()]);
         $idField->getName();
+        
         $nameField = new Field(['name' => 'name', 'type' => new StringType()]);
 
         $this->assertEquals([
diff --git a/tests/Library/Field/FieldTest.php b/tests/Library/Field/FieldTest.php
index e6f62f91..e55f0a2e 100644
--- a/tests/Library/Field/FieldTest.php
+++ b/tests/Library/Field/FieldTest.php
@@ -24,7 +24,7 @@
 class FieldTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInlineFieldCreation()
+    public function testInlineFieldCreation(): void
     {
         $field = new Field([
             'name' => 'id',
@@ -38,7 +38,7 @@ public function testInlineFieldCreation()
         $fieldWithResolve = new Field([
             'name'    => 'title',
             'type'    => new StringType(),
-            'resolve' => function ($value, array $args, ResolveInfo $info) {
+            'resolve' => static function ($value, array $args, ResolveInfo $info) {
                 return $info->getReturnType()->serialize($value);
             }
         ]);
@@ -50,7 +50,7 @@ public function testInlineFieldCreation()
 
     }
 
-    public function testObjectFieldCreation()
+    public function testObjectFieldCreation(): void
     {
         $field = new TestField();
         $resolveInfo = TestResolveInfo::createTestResolveInfo($field);
@@ -61,7 +61,7 @@ public function testObjectFieldCreation()
         $this->assertEquals('test', $field->resolve('test', [], $resolveInfo));
     }
 
-    public function testArgumentsTrait()
+    public function testArgumentsTrait(): void
     {
         $testField = new TestField();
         $this->assertFalse($testField->hasArguments());
@@ -89,7 +89,7 @@ public function testArgumentsTrait()
      * @dataProvider invalidFieldProvider
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidFieldParams($fieldConfig)
+    public function testInvalidFieldParams($fieldConfig): void
     {
         $field = new Field($fieldConfig);
         ConfigValidator::getInstance()->assertValidConfig($field->getConfig());
diff --git a/tests/Library/Field/InputFieldTest.php b/tests/Library/Field/InputFieldTest.php
index cd43ed68..b56cc29d 100644
--- a/tests/Library/Field/InputFieldTest.php
+++ b/tests/Library/Field/InputFieldTest.php
@@ -25,7 +25,7 @@
 class InputFieldTest extends \PHPUnit_Framework_TestCase
 {
 
-    private $introspectionQuery = <<<TEXT
+    private string $introspectionQuery = <<<TEXT
 
 query IntrospectionQuery {
                 __schema {
@@ -105,7 +105,7 @@ enumValues {
             }
 TEXT;
 
-    public function testFieldWithInputFieldArgument()
+    public function testFieldWithInputFieldArgument(): void
     {
         $schema    = new Schema([
             'query' => new ObjectType([
@@ -133,7 +133,7 @@ public function testFieldWithInputFieldArgument()
         $processor->processPayload($this->introspectionQuery);
     }
 
-    public function testInlineInputFieldCreation()
+    public function testInlineInputFieldCreation(): void
     {
         $field = new InputField([
             'name'         => 'id',
@@ -149,7 +149,7 @@ public function testInlineInputFieldCreation()
     }
 
 
-    public function testObjectInputFieldCreation()
+    public function testObjectInputFieldCreation(): void
     {
         $field = new TestInputField();
 
@@ -159,7 +159,7 @@ public function testObjectInputFieldCreation()
         $this->assertEquals('default', $field->getDefaultValue());
     }
 
-    public function testListAsInputField()
+    public function testListAsInputField(): void
     {
         new InputField([
             'name' => 'test',
@@ -171,7 +171,7 @@ public function testListAsInputField()
      * @dataProvider invalidInputFieldProvider
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidInputFieldParams($fieldConfig)
+    public function testInvalidInputFieldParams($fieldConfig): void
     {
         $field = new InputField($fieldConfig);
         ConfigValidator::getInstance()->assertValidConfig($field->getConfig());
diff --git a/tests/Library/Relay/ArrayConnectionTest.php b/tests/Library/Relay/ArrayConnectionTest.php
index fd663978..6128770b 100644
--- a/tests/Library/Relay/ArrayConnectionTest.php
+++ b/tests/Library/Relay/ArrayConnectionTest.php
@@ -12,7 +12,7 @@
 
 class ArrayConnectionTest extends \PHPUnit_Framework_TestCase
 {
-    public function testCursors()
+    public function testCursors(): void
     {
         $offset = 3;
         $data   = ['a', 'b', 'c', 'd', 'e'];
@@ -26,7 +26,7 @@ public function testCursors()
         $this->assertEquals(2, ArrayConnection::cursorToOffsetWithDefault(null, 2));
     }
 
-    public function testConnectionDefinition()
+    public function testConnectionDefinition(): void
     {
         $data  = ['a', 'b', 'c', 'd', 'e'];
         $edges = [];
diff --git a/tests/Library/Relay/CallableFetcherTest.php b/tests/Library/Relay/CallableFetcherTest.php
index 044693d6..578f8d47 100644
--- a/tests/Library/Relay/CallableFetcherTest.php
+++ b/tests/Library/Relay/CallableFetcherTest.php
@@ -14,9 +14,13 @@
 
 class CallableFetcherTest extends \PHPUnit_Framework_TestCase
 {
-    public function testMethods()
+    public function testMethods(): void
     {
-        $fetcher = new CallableFetcher(function ($type, $id) { return ['name' => $type . ' Name', 'id' => $id]; }, function ($object) { return $object; });
+        $fetcher = new CallableFetcher(static function (string $type, $id) : array {
+            return ['name' => $type . ' Name', 'id' => $id];
+        }, static function ($object) {
+            return $object;
+        });
         $this->assertEquals([
             'name' => 'User Name',
             'id'   => 12
diff --git a/tests/Library/Relay/ConnectionTest.php b/tests/Library/Relay/ConnectionTest.php
index adbd5867..bdd14020 100644
--- a/tests/Library/Relay/ConnectionTest.php
+++ b/tests/Library/Relay/ConnectionTest.php
@@ -18,7 +18,7 @@
 class ConnectionTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testConnectionArgs()
+    public function testConnectionArgs(): void
     {
         $this->assertEquals([
             'after'  => ['type' => TypeMap::TYPE_STRING],
@@ -29,7 +29,7 @@ public function testConnectionArgs()
         ], Connection::connectionArgs());
     }
 
-    public function testPageInfoType()
+    public function testPageInfoType(): void
     {
         $type = new PageInfoType();
         $this->assertEquals('PageInfo', $type->getName());
@@ -40,7 +40,7 @@ public function testPageInfoType()
         $this->assertTrue($type->hasField('endCursor'));
     }
 
-    public function testEdgeDefinition()
+    public function testEdgeDefinition(): void
     {
         $edgeType = Connection::edgeDefinition(new StringType(), 'user');
         $this->assertEquals('userEdge', $edgeType->getName());
@@ -48,7 +48,7 @@ public function testEdgeDefinition()
         $this->assertTrue($edgeType->hasField('cursor'));
     }
 
-    public function testConnectionDefinition()
+    public function testConnectionDefinition(): void
     {
         $connection = Connection::connectionDefinition(new TestObjectType(), 'user');
         $this->assertEquals($connection->getName(), 'userConnection');
diff --git a/tests/Library/Relay/GlobalIdFieldTest.php b/tests/Library/Relay/GlobalIdFieldTest.php
index ddea8876..30f3fa87 100644
--- a/tests/Library/Relay/GlobalIdFieldTest.php
+++ b/tests/Library/Relay/GlobalIdFieldTest.php
@@ -16,7 +16,7 @@
 class GlobalIdFieldTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testSimpleMethods()
+    public function testSimpleMethods(): void
     {
         $typeName = 'user';
         $field    = new GlobalIdField($typeName);
diff --git a/tests/Library/Relay/MutationTest.php b/tests/Library/Relay/MutationTest.php
index 353a93ff..833beddd 100644
--- a/tests/Library/Relay/MutationTest.php
+++ b/tests/Library/Relay/MutationTest.php
@@ -17,15 +17,14 @@
 class MutationTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testCreation()
+    public function testCreation(): void
     {
         $mutation = RelayMutation::buildMutation('ship', [
             'name' => new StringType()
         ],[
             'id' => new IdType(),
             'name' => new StringType()
-        ], function($source, $args, $info) {
-
+        ], static function ($source, $args, $info) : void {
         });
         $this->assertEquals('ship', $mutation->getName());
     }
@@ -33,11 +32,12 @@ public function testCreation()
     /**
      * @expectedException \Exception
      */
-    public function testInvalidType()
+    public function testInvalidType(): void
     {
         RelayMutation::buildMutation('ship', [
             'name' => new StringType()
-        ], new IntType(), function($source, $args, $info) {});
+        ], new IntType(), static function ($source, $args, $info) : void {
+        });
 
     }
 
diff --git a/tests/Library/Relay/NodeFieldTest.php b/tests/Library/Relay/NodeFieldTest.php
index 96bab0d3..51bfd401 100644
--- a/tests/Library/Relay/NodeFieldTest.php
+++ b/tests/Library/Relay/NodeFieldTest.php
@@ -15,9 +15,11 @@
 class NodeFieldTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testMethods()
+    public function testMethods(): void
     {
-        $fetcher = new CallableFetcher(function () { }, function () { });
+        $fetcher = new CallableFetcher(static function () : void {
+        }, static function () : void {
+        });
         $field   = new NodeField($fetcher);
 
         $this->assertEquals('Fetches an object given its ID', $field->getDescription());
diff --git a/tests/Library/Relay/NodeInterfaceTypeTest.php b/tests/Library/Relay/NodeInterfaceTypeTest.php
index 46bfcf5e..ecbf9d34 100644
--- a/tests/Library/Relay/NodeInterfaceTypeTest.php
+++ b/tests/Library/Relay/NodeInterfaceTypeTest.php
@@ -15,7 +15,7 @@
 class NodeInterfaceTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testMethods()
+    public function testMethods(): void
     {
         $type       = new NodeInterfaceType();
         $testObject = new TestObjectType();
@@ -25,7 +25,10 @@ public function testMethods()
         $this->assertNull($type->getFetcher());
         $this->assertNull($type->resolveType($testObject));
 
-        $fetcher = new CallableFetcher(function () { }, function () { return new TestObjectType(); });
+        $fetcher = new CallableFetcher(static function () : void {
+        }, static function () : \Youshido\Tests\DataProvider\TestObjectType {
+            return new TestObjectType();
+        });
         $type->setFetcher($fetcher);
         $this->assertEquals($fetcher, $type->getFetcher());
 
diff --git a/tests/Library/Relay/NodeTest.php b/tests/Library/Relay/NodeTest.php
index a9476b6b..79dd25b0 100644
--- a/tests/Library/Relay/NodeTest.php
+++ b/tests/Library/Relay/NodeTest.php
@@ -14,7 +14,7 @@
 
 class NodeTest extends \PHPUnit_Framework_TestCase
 {
-    public function testMethods()
+    public function testMethods(): void
     {
         $global     = Node::toGlobalId('user', 1);
         $fromGlobal = Node::fromGlobalId($global);
@@ -35,7 +35,7 @@ public function malformedIdProvider()
     /**
      * @dataProvider malformedIdProvider
      */
-    public function testFromGlobalIdThrowsExceptionIfGivenMalformedId($idToCheck)
+    public function testFromGlobalIdThrowsExceptionIfGivenMalformedId($idToCheck): void
     {
         $this->setExpectedException(InvalidArgumentException::class);
         Node::fromGlobalId($idToCheck);
diff --git a/tests/Library/Type/EnumTypeTest.php b/tests/Library/Type/EnumTypeTest.php
index c6969712..8ef8d3b3 100644
--- a/tests/Library/Type/EnumTypeTest.php
+++ b/tests/Library/Type/EnumTypeTest.php
@@ -19,7 +19,7 @@ class EnumTypeTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidInlineCreation()
+    public function testInvalidInlineCreation(): void
     {
         new EnumType([]);
     }
@@ -27,7 +27,7 @@ public function testInvalidInlineCreation()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidEmptyParams()
+    public function testInvalidEmptyParams(): void
     {
         $enumField = new EnumType([
             'values' => []
@@ -39,7 +39,7 @@ public function testInvalidEmptyParams()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidValueParams()
+    public function testInvalidValueParams(): void
     {
         $enumField = new EnumType([
             'values' => [
@@ -53,7 +53,7 @@ public function testInvalidValueParams()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testExistingNameParams()
+    public function testExistingNameParams(): void
     {
         $enumField = new EnumType([
             'values' => [
@@ -69,7 +69,7 @@ public function testExistingNameParams()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidNameParams()
+    public function testInvalidNameParams(): void
     {
         $enumField = new EnumType([
             'values' => [
@@ -85,7 +85,7 @@ public function testInvalidNameParams()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testWithoutValueParams()
+    public function testWithoutValueParams(): void
     {
         $enumField = new EnumType([
             'values' => [
@@ -97,7 +97,7 @@ public function testWithoutValueParams()
         ConfigValidator::getInstance()->assertValidConfig($enumField->getConfig());
     }
 
-    public function testNormalCreatingParams()
+    public function testNormalCreatingParams(): void
     {
         $valuesData = [
             [
@@ -132,7 +132,7 @@ public function testNormalCreatingParams()
         $this->assertEquals($valuesData, $enumType->getValues());
     }
 
-    public function testExtendedObject()
+    public function testExtendedObject(): void
     {
         $testEnumType = new TestEnumType();
         $this->assertEquals('TestEnum', $testEnumType->getName());
diff --git a/tests/Library/Type/InputObjectTypeTest.php b/tests/Library/Type/InputObjectTypeTest.php
index 09320fad..1ad99c23 100644
--- a/tests/Library/Type/InputObjectTypeTest.php
+++ b/tests/Library/Type/InputObjectTypeTest.php
@@ -25,7 +25,7 @@
 class InputObjectTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInternal()
+    public function testInternal(): void
     {
         $inputObjectType = new InputObjectType([
             'name'   => 'PostData',
@@ -41,13 +41,13 @@ public function testInternal()
         $this->assertFalse($inputObjectType->isValidValue(['title' => null]));
     }
 
-    public function testStandaloneClass()
+    public function testStandaloneClass(): void
     {
         $inputObjectType = new TestInputObjectType();
         $this->assertEquals('TestInputObject', $inputObjectType->getName());
     }
 
-    public function testListOfInputWithNonNull()
+    public function testListOfInputWithNonNull(): void
     {
         $processor = new Processor(new Schema([
             'query'    => new ObjectType([
@@ -55,7 +55,7 @@ public function testListOfInputWithNonNull()
                 'fields' => [
                     'empty' => [
                         'type'    => new StringType(),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ]
@@ -74,7 +74,7 @@ public function testListOfInputWithNonNull()
                             ]))
                         ],
                         'type'    => new BooleanType(),
-                        'resolve' => function ($object, $args) {
+                        'resolve' => static function ($object, $args) : bool {
                             return true;
                         }
                     ]
@@ -100,7 +100,7 @@ public function testListOfInputWithNonNull()
         );
     }
 
-    public function testNullableInputWithNonNull()
+    public function testNullableInputWithNonNull(): void
     {
         $processor = new Processor(new Schema([
             'query'    => new ObjectType([
@@ -108,7 +108,7 @@ public function testNullableInputWithNonNull()
                 'fields' => [
                     'empty' => [
                         'type'    => new StringType(),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ]
@@ -127,7 +127,7 @@ public function testNullableInputWithNonNull()
                             ])
                         ],
                         'type'    => new BooleanType(),
-                        'resolve' => function ($object, $args) {
+                        'resolve' => static function ($object, $args) : bool {
                             return true;
                         }
                     ]
@@ -143,7 +143,7 @@ public function testNullableInputWithNonNull()
         );
     }
 
-    public function testListInsideInputObject()
+    public function testListInsideInputObject(): void
     {
         $processor = new Processor(new Schema([
             'query'    => new ObjectType([
@@ -151,7 +151,7 @@ public function testListInsideInputObject()
                 'fields' => [
                     'empty' => [
                         'type'    => new StringType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : void {
                         }
                     ],
                 ]
@@ -174,7 +174,7 @@ public function testListInsideInputObject()
                                 ]
                             ])
                         ],
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'success message';
                         }
                     ]
@@ -200,7 +200,7 @@ public function testListInsideInputObject()
         $this->assertEquals(['data' => ['createList' => 'success message']], $processor->getResponseData());
     }
 
-    public function testInputObjectDefaultValue()
+    public function testInputObjectDefaultValue(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -223,7 +223,7 @@ public function testInputObjectDefaultValue()
                                 ],
                             ],
                         ],
-                        'resolve' => function ($source, $args) {
+                        'resolve' => static function ($source, array $args) : array {
                             return [
                                 'limit is ' . $args['paging']['limit'],
                                 'offset is ' . $args['paging']['offset'],
@@ -235,6 +235,7 @@ public function testInputObjectDefaultValue()
             ]),
         ]));
         $processor->processPayload('{ cities }');
+        
         $response = $processor->getResponseData();
         $this->assertEquals(
             [
@@ -247,7 +248,7 @@ public function testInputObjectDefaultValue()
         );
     }
 
-    public function testInvalidTypeErrors()
+    public function testInvalidTypeErrors(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -270,7 +271,7 @@ public function testInvalidTypeErrors()
                                 ]
                             ]),
                         ],
-                        'resolve' => function ($source, $args) {
+                        'resolve' => static function ($source, array $args) : string {
                             return sprintf('%s by %s', $args['title'], $args['userId']);
                         }
                     ],
@@ -279,6 +280,7 @@ public function testInvalidTypeErrors()
             ]),
         ]));
         $processor->processPayload('mutation { createPost(object: {title: "Hello world"}) }');
+        
         $response = $processor->getResponseData();
         $this->assertEquals(
             [
diff --git a/tests/Library/Type/InterfaceTypeTest.php b/tests/Library/Type/InterfaceTypeTest.php
index 1f444f7b..82a93caf 100644
--- a/tests/Library/Type/InterfaceTypeTest.php
+++ b/tests/Library/Type/InterfaceTypeTest.php
@@ -19,7 +19,7 @@
 class InterfaceTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInterfaceMethods()
+    public function testInterfaceMethods(): void
     {
         $interface = new TestInterfaceType();
         $this->assertEquals($interface->getNamedType(), $interface->getType());
@@ -47,7 +47,7 @@ public function testInterfaceMethods()
             'fields'      => [
                 'name' => new StringType()
             ],
-            'resolveType' => function ($object) {
+            'resolveType' => static function ($object) {
                 return $object;
             }
         ]);
@@ -59,7 +59,7 @@ public function testInterfaceMethods()
         $this->assertFalse($interfaceType->isValidValue('invalid object'));
     }
 
-    public function testApplyInterface()
+    public function testApplyInterface(): void
     {
         $extendedType = new TestExtendedType();
 
diff --git a/tests/Library/Type/ListTypeTest.php b/tests/Library/Type/ListTypeTest.php
index fdeb3516..d4f57f12 100644
--- a/tests/Library/Type/ListTypeTest.php
+++ b/tests/Library/Type/ListTypeTest.php
@@ -17,7 +17,7 @@
 class ListTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInline()
+    public function testInline(): void
     {
         $listType = new ListType(new StringType());
         $this->assertEquals(new StringType(), $listType->getNamedType());
@@ -27,13 +27,13 @@ public function testInline()
         $this->assertFalse($listType->isValidValue('invalid value'));
     }
 
-    public function testStandaloneClass()
+    public function testStandaloneClass(): void
     {
         $listType = new TestListType();
         $this->assertEquals(new StringType(), $listType->getNamedType());
     }
 
-    public function testListOfInputsWithArguments()
+    public function testListOfInputsWithArguments(): void
     {
 
     }
diff --git a/tests/Library/Type/NonNullTypeTest.php b/tests/Library/Type/NonNullTypeTest.php
index c8c80346..eba972e3 100644
--- a/tests/Library/Type/NonNullTypeTest.php
+++ b/tests/Library/Type/NonNullTypeTest.php
@@ -20,12 +20,12 @@ class NonNullTypeTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidParams()
+    public function testInvalidParams(): void
     {
         new NonNullType('invalid param');
     }
 
-    public function testNonNullType()
+    public function testNonNullType(): void
     {
         $stringType      = new StringType();
         $nonNullType     = new NonNullType(new StringType());
diff --git a/tests/Library/Type/ObjectTypeTest.php b/tests/Library/Type/ObjectTypeTest.php
index 43382480..53b63c33 100644
--- a/tests/Library/Type/ObjectTypeTest.php
+++ b/tests/Library/Type/ObjectTypeTest.php
@@ -24,7 +24,7 @@ class ObjectTypeTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testCreatingInvalidObject()
+    public function testCreatingInvalidObject(): void
     {
         new ObjectType([]);
     }
@@ -32,7 +32,7 @@ public function testCreatingInvalidObject()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidNameParam()
+    public function testInvalidNameParam(): void
     {
         $type = new ObjectType([
             'name' => null
@@ -43,7 +43,7 @@ public function testInvalidNameParam()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidFieldsParam()
+    public function testInvalidFieldsParam(): void
     {
         $type = new ObjectType([
             'name'   => 'SomeName',
@@ -55,7 +55,7 @@ public function testInvalidFieldsParam()
     /**
      * @expectedException \InvalidArgumentException
      */
-    public function testSerialize()
+    public function testSerialize(): void
     {
         $object = new ObjectType([
             'name'   => 'SomeName',
@@ -67,7 +67,7 @@ public function testSerialize()
     }
 
 
-    public function testNormalCreatingParam()
+    public function testNormalCreatingParam(): void
     {
         $objectType = new ObjectType([
             'name'        => 'Post',
@@ -89,7 +89,7 @@ public function testNormalCreatingParam()
         $this->assertEquals('Post type description', $objectType->getDescription());
     }
 
-    public function testFieldsTrait()
+    public function testFieldsTrait(): void
     {
         $idField = new Field(['name' => 'id', 'type' => new IntType()]);
         $nameField = new Field(['name' => 'name', 'type' => new StringType()]);
@@ -113,7 +113,7 @@ public function testFieldsTrait()
         ], $objectType->getFields());
     }
 
-    public function testExtendedClass()
+    public function testExtendedClass(): void
     {
         $objectType = new TestObjectType();
         $this->assertEquals($objectType->getName(), 'TestObject');
@@ -122,7 +122,7 @@ public function testExtendedClass()
         $this->assertNull($objectType->getDescription());
     }
 
-    public function testMutationObjectClass()
+    public function testMutationObjectClass(): void
     {
         $mutation = new TestMutationObjectType();
         $this->assertEquals(new StringType(), $mutation->getType());
diff --git a/tests/Library/Type/ScalarExtendTypeTest.php b/tests/Library/Type/ScalarExtendTypeTest.php
index 23ab0b57..b6ad8810 100644
--- a/tests/Library/Type/ScalarExtendTypeTest.php
+++ b/tests/Library/Type/ScalarExtendTypeTest.php
@@ -18,7 +18,7 @@
 class ScalarExtendTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testType()
+    public function testType(): void
     {
         $reportType = new ObjectType([
             'name'   => 'Report',
@@ -33,7 +33,7 @@ public function testType()
                     'fields' => [
                         'latestReport' => [
                             'type'    => $reportType,
-                            'resolve' => function () {
+                            'resolve' => static function () : array {
                                 return [
                                     'title' => 'Accident #1',
                                     'time'  => '13:30:12',
diff --git a/tests/Library/Type/ScalarTypeTest.php b/tests/Library/Type/ScalarTypeTest.php
index a50e0fea..94c6095e 100644
--- a/tests/Library/Type/ScalarTypeTest.php
+++ b/tests/Library/Type/ScalarTypeTest.php
@@ -18,7 +18,7 @@
 class ScalarTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testScalarPrimitives()
+    public function testScalarPrimitives(): void
     {
         foreach (TypeFactory::getScalarTypesNames() as $typeName) {
             $scalarType     = TypeFactory::getScalarType($typeName);
@@ -32,7 +32,7 @@ public function testScalarPrimitives()
             $this->assertEquals($scalarType->getType(), $scalarType->getNamedType());
             $this->assertNull($scalarType->getConfig());
 
-            foreach (call_user_func(['Youshido\Tests\DataProvider\TestScalarDataProvider', $testDataMethod]) as list($data, $serialized, $isValid)) {
+            foreach (call_user_func([\Youshido\Tests\DataProvider\TestScalarDataProvider::class, $testDataMethod]) as list($data, $serialized, $isValid)) {
 
                 $this->assertSerialization($scalarType, $data, $serialized);
                 $this->assertParse($scalarType, $data, $serialized, $typeName);
@@ -44,27 +44,29 @@ public function testScalarPrimitives()
                 }
             }
         }
+        
         try {
             TypeFactory::getScalarType('invalid type');
-        } catch (\Exception $e) {
-            $this->assertEquals('Configuration problem with type invalid type', $e->getMessage());
+        } catch (\Exception $exception) {
+            $this->assertEquals('Configuration problem with type invalid type', $exception->getMessage());
         }
+        
         $this->assertEquals('String', (string)new StringType());
 
     }
 
-    public function testDateTimeType()
+    public function testDateTimeType(): void
     {
         $dateType = new DateTimeType('Y/m/d H:i:s');
         $this->assertEquals('2016/05/31 12:00:00', $dateType->serialize(new \DateTimeImmutable('2016-05-31 12:00pm')));
     }
 
-    private function assertSerialization(AbstractScalarType $object, $input, $expected)
+    private function assertSerialization(AbstractScalarType $object, $input, $expected): void
     {
         $this->assertEquals($expected, $object->serialize($input), $object->getName() . ' serialize for: ' . serialize($input));
     }
 
-    private function assertParse(AbstractScalarType $object, $input, $expected, $typeName)
+    private function assertParse(AbstractScalarType $object, $input, $expected, $typeName): void
     {
         $parsed = $object->parseValue($input);
         if ($parsed instanceof \DateTime) {
diff --git a/tests/Library/Type/SchemaDirectivesListTest.php b/tests/Library/Type/SchemaDirectivesListTest.php
index 42d95aa5..6d28e138 100644
--- a/tests/Library/Type/SchemaDirectivesListTest.php
+++ b/tests/Library/Type/SchemaDirectivesListTest.php
@@ -7,7 +7,7 @@
 
 class SchemaDirectivesListTest extends \PHPUnit_Framework_TestCase
 {
-    public function testCanAddASingleDirective()
+    public function testCanAddASingleDirective(): void
     {
         $directiveList = new SchemaDirectivesList();
         $directiveList->addDirective(
@@ -18,7 +18,7 @@ public function testCanAddASingleDirective()
         $this->assertTrue($directiveList->isDirectiveNameRegistered('testDirective'));
     }
 
-    public function testCanAddMultipleDirectives()
+    public function testCanAddMultipleDirectives(): void
     {
         $directiveList = new SchemaDirectivesList();
         $directiveList->addDirectives([
@@ -33,7 +33,7 @@ public function testCanAddMultipleDirectives()
         $this->assertTrue($directiveList->isDirectiveNameRegistered('testDirectiveTwo'));
     }
 
-    public function testItThrowsExceptionWhenAddingInvalidDirectives()
+    public function testItThrowsExceptionWhenAddingInvalidDirectives(): void
     {
         $this->setExpectedException(\Exception::class, "addDirectives accept only array of directives");
         $directiveList = new SchemaDirectivesList();
diff --git a/tests/Library/Type/UnionTypeTest.php b/tests/Library/Type/UnionTypeTest.php
index 00dbb300..13789f9f 100644
--- a/tests/Library/Type/UnionTypeTest.php
+++ b/tests/Library/Type/UnionTypeTest.php
@@ -18,7 +18,7 @@
 class UnionTypeTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testInlineCreation()
+    public function testInlineCreation(): void
     {
         $object = new ObjectType([
             'name' => 'TestObject',
@@ -32,7 +32,7 @@ public function testInlineCreation()
                 new TestObjectType(),
                 $object
             ],
-            'resolveType' => function ($type) {
+            'resolveType' => static function ($type) {
                 return $type;
             }
         ]);
@@ -46,7 +46,7 @@ public function testInlineCreation()
         $this->assertTrue($type->isValidValue(true));
     }
 
-    public function testObjectCreation()
+    public function testObjectCreation(): void
     {
         $type = new TestUnionType();
 
@@ -59,7 +59,7 @@ public function testObjectCreation()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidTypesWithScalar()
+    public function testInvalidTypesWithScalar(): void
     {
         $type = new UnionType([
             'name'        => 'Car',
@@ -67,7 +67,7 @@ public function testInvalidTypesWithScalar()
             'types'       => [
                 'test', new IntType()
             ],
-            'resolveType' => function ($type) {
+            'resolveType' => static function ($type) {
                 return $type;
             }
         ]);
@@ -77,7 +77,7 @@ public function testInvalidTypesWithScalar()
     /**
      * @expectedException Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidTypes()
+    public function testInvalidTypes(): void
     {
         $type = new UnionType([
             'name'        => 'Car',
@@ -85,7 +85,7 @@ public function testInvalidTypes()
             'types'       => [
                 new IntType()
             ],
-            'resolveType' => function ($type) {
+            'resolveType' => static function ($type) {
                 return $type;
             }
         ]);
diff --git a/tests/Library/Utilities/ErrorContainerTraitTest.php b/tests/Library/Utilities/ErrorContainerTraitTest.php
index 519fee3d..7bcf9a94 100644
--- a/tests/Library/Utilities/ErrorContainerTraitTest.php
+++ b/tests/Library/Utilities/ErrorContainerTraitTest.php
@@ -25,7 +25,7 @@ protected function setUp()
         $this->clearErrors();
     }
 
-    public function testAddHasClearMergeErrors()
+    public function testAddHasClearMergeErrors(): void
     {
         $error = new \Exception('Error');
         $this->addError($error);
@@ -41,7 +41,7 @@ public function testAddHasClearMergeErrors()
         $this->assertEquals([$error, $error], $this->getErrors());
     }
 
-    public function testGetErrorsAsArrayGenericExceptionWithoutCode()
+    public function testGetErrorsAsArrayGenericExceptionWithoutCode(): void
     {
         // Code is zero by default
         $this->addError(new \Exception('Generic exception'));
@@ -52,7 +52,7 @@ public function testGetErrorsAsArrayGenericExceptionWithoutCode()
         ], $this->getErrorsArray());
     }
 
-    public function testGetErrorsAsArrayGenericExceptionWithCode()
+    public function testGetErrorsAsArrayGenericExceptionWithCode(): void
     {
         $this->addError(new \Exception('Generic exception with code', 4));
         $this->assertEquals([
@@ -63,7 +63,7 @@ public function testGetErrorsAsArrayGenericExceptionWithCode()
         ], $this->getErrorsArray());
     }
 
-    public function testGetErrorsAsArrayLocationableException()
+    public function testGetErrorsAsArrayLocationableException(): void
     {
         $this->addError(new SyntaxErrorException('Syntax error', new Location(5, 88)));
         $this->assertEquals([
@@ -79,7 +79,7 @@ public function testGetErrorsAsArrayLocationableException()
         ], $this->getErrorsArray());
     }
 
-    public function testGetErrorsAsArrayExtendedException()
+    public function testGetErrorsAsArrayExtendedException(): void
     {
         $this->addError(new ExtendedException('Extended exception'));
         $this->assertEquals([
@@ -93,7 +93,7 @@ public function testGetErrorsAsArrayExtendedException()
         ], $this->getErrorsArray());
     }
 
-    public function testGetErrorsAsArrayExceptionWithEverything()
+    public function testGetErrorsAsArrayExceptionWithEverything(): void
     {
         $this->addError(new SuperException('Super exception', 3));
         $this->assertEquals([
@@ -117,7 +117,7 @@ public function testGetErrorsAsArrayExceptionWithEverything()
 
 class ExtendedException extends \Exception implements ExtendedExceptionInterface
 {
-    public function getExtensions()
+    public function getExtensions(): array
     {
         return [
             'foo' => 'foo',
@@ -128,7 +128,7 @@ public function getExtensions()
 
 class SuperException extends \Exception implements LocationableExceptionInterface, ExtendedExceptionInterface
 {
-    public function getExtensions()
+    public function getExtensions(): array
     {
         return [
             'foo' => 'foo',
@@ -136,7 +136,7 @@ public function getExtensions()
         ];
     }
 
-    public function getLocation()
+    public function getLocation(): \Youshido\GraphQL\Parser\Location
     {
         return new Location(6, 10);
     }
diff --git a/tests/Library/Utilities/TypeUtilitiesTest.php b/tests/Library/Utilities/TypeUtilitiesTest.php
index f0c33f07..6340be52 100644
--- a/tests/Library/Utilities/TypeUtilitiesTest.php
+++ b/tests/Library/Utilities/TypeUtilitiesTest.php
@@ -18,7 +18,7 @@
 class TypeUtilitiesTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testTypeService()
+    public function testTypeService(): void
     {
         $this->assertTrue(TypeService::isScalarType(TypeMap::TYPE_STRING));
         $this->assertFalse(TypeService::isScalarType('gibberish'));
@@ -35,12 +35,12 @@ public function testTypeService()
     /**
      * @expectedException \Exception
      */
-    public function testNamedTypeResolverException()
+    public function testNamedTypeResolverException(): void
     {
         TypeService::resolveNamedType(['name' => 'test']);
     }
 
-    public function testIsInputType()
+    public function testIsInputType(): void
     {
         $testType = new ObjectType(['name' => 'test', 'fields' => ['name' => new StringType()]]);
         $this->assertTrue(TypeService::isInputType(new StringType()));
@@ -49,14 +49,14 @@ public function testIsInputType()
         $this->assertFalse(TypeService::isInputType($testType));
     }
 
-    public function testIsAbstractType()
+    public function testIsAbstractType(): void
     {
         $this->assertTrue(TypeService::isAbstractType(new TestInterfaceType()));
         $this->assertFalse(TypeService::isAbstractType(new StringType()));
         $this->assertFalse(TypeService::isAbstractType('invalid type'));
     }
 
-    public function testGetPropertyValue() {
+    public function testGetPropertyValue(): void {
         $arrayData = (new TestObjectType())->getData();
 
         // Test with arrays
@@ -80,22 +80,22 @@ public function testGetPropertyValue() {
  */
 class ObjectWithVariousGetters
 {
-    public function getName()
+    public function getName(): string
     {
         return 'John';
     }
 
-    public function getNamedAfter()
+    public function getNamedAfter(): string
     {
         return 'John Doe';
     }
 
-    public function isTrue()
+    public function isTrue(): bool
     {
         return true;
     }
 
-    public function isFalse()
+    public function isFalse(): bool
     {
         return false;
     }
diff --git a/tests/Library/Validator/RequestValidatorTest.php b/tests/Library/Validator/RequestValidatorTest.php
index bff813e1..270334ed 100644
--- a/tests/Library/Validator/RequestValidatorTest.php
+++ b/tests/Library/Validator/RequestValidatorTest.php
@@ -25,10 +25,8 @@ class RequestValidatorTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException \Youshido\GraphQL\Exception\Parser\InvalidRequestException
      * @dataProvider invalidRequestProvider
-     *
-     * @param Request $request
      */
-    public function testInvalidRequests(Request $request)
+    public function testInvalidRequests(Request $request): void
     {
         (new RequestValidator())->validate($request);
     }
diff --git a/tests/Library/Validator/SchemaValidatorTest.php b/tests/Library/Validator/SchemaValidatorTest.php
index 220c3e03..9f769f23 100644
--- a/tests/Library/Validator/SchemaValidatorTest.php
+++ b/tests/Library/Validator/SchemaValidatorTest.php
@@ -23,7 +23,7 @@ class SchemaValidatorTest extends \PHPUnit_Framework_TestCase
     /**
      * @expectedException \Youshido\GraphQL\Exception\ConfigurationException
      */
-    public function testInvalidSchema()
+    public function testInvalidSchema(): void
     {
         $validator = new SchemaValidator();
         $validator->validate(new TestEmptySchema());
@@ -33,7 +33,7 @@ public function testInvalidSchema()
      * @expectedException \Youshido\GraphQL\Exception\ConfigurationException
      * @expectedExceptionMessage Implementation of TestInterface is invalid for the field name
      */
-    public function testInvalidInterfacesSimpleType()
+    public function testInvalidInterfacesSimpleType(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -58,7 +58,7 @@ public function testInvalidInterfacesSimpleType()
      * @expectedException \Youshido\GraphQL\Exception\ConfigurationException
      * @expectedExceptionMessage Implementation of TestInterface is invalid for the field name
      */
-    public function testInvalidInterfacesCompositeType()
+    public function testInvalidInterfacesCompositeType(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -83,7 +83,7 @@ public function testInvalidInterfacesCompositeType()
      * @expectedException \Youshido\GraphQL\Exception\ConfigurationException
      * @expectedExceptionMessage Implementation of TestInterface is invalid for the field name
      */
-    public function testInvalidInterfaces()
+    public function testInvalidInterfaces(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -104,7 +104,7 @@ public function testInvalidInterfaces()
         $validator->validate($schema);
     }
 
-    public function testValidSchema()
+    public function testValidSchema(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -126,7 +126,7 @@ public function testValidSchema()
         try {
             $validator->validate($schema);
             $this->assertTrue(true);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             $this->assertTrue(false);
         }
     }
diff --git a/tests/Library/Validator/TypeValidationRuleTest.php b/tests/Library/Validator/TypeValidationRuleTest.php
index 57e368e1..2e667d34 100644
--- a/tests/Library/Validator/TypeValidationRuleTest.php
+++ b/tests/Library/Validator/TypeValidationRuleTest.php
@@ -40,7 +40,7 @@ protected function setUp()
      *
      * @dataProvider simpleRulesProvider
      */
-    public function testSimpleRules($ruleInfo, $data, $isValid = true)
+    public function testSimpleRules($ruleInfo, $data, $isValid = true): void
     {
         $this->assertEquals($isValid, $this->rule->validate($data, $ruleInfo));
     }
@@ -55,7 +55,8 @@ public function simpleRulesProvider()
             [TypeService::TYPE_ANY_OBJECT, new StringType()],
             [TypeService::TYPE_ANY_OBJECT, null, false],
 
-            [TypeService::TYPE_CALLABLE, function () { }],
+            [TypeService::TYPE_CALLABLE, static function () : void {
+            }],
             [TypeService::TYPE_CALLABLE, null, false],
 
             [TypeService::TYPE_BOOLEAN, true],
@@ -84,7 +85,7 @@ public function simpleRulesProvider()
      *
      * @dataProvider complexRuleProvider
      */
-    public function testComplexRules($ruleInfo, $data, $isValid = true)
+    public function testComplexRules($ruleInfo, $data, $isValid = true): void
     {
         $this->assertEquals($isValid, $this->rule->validate($data, $ruleInfo));
     }
diff --git a/tests/Parser/AstTest.php b/tests/Parser/AstTest.php
index 49a8ae92..15bcde1c 100644
--- a/tests/Parser/AstTest.php
+++ b/tests/Parser/AstTest.php
@@ -23,7 +23,7 @@
 class AstTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testArgument()
+    public function testArgument(): void
     {
         $argument = new Argument('test', new Literal('test', new Location(1,1)), new Location(1,1));
 
@@ -37,7 +37,7 @@ public function testArgument()
         $this->assertEquals($argument->getValue(), 'some value');
     }
 
-    public function testField()
+    public function testField(): void
     {
         $field = new Field('field', null, [], [], new Location(1,1));
 
@@ -55,7 +55,7 @@ public function testField()
         $this->assertEquals(['argument' => 'argument value'], $field->getKeyValueArguments());
     }
 
-    public function testFragment()
+    public function testFragment(): void
     {
         $fields = [
             new Field('field', null, [], [], new Location(1,1))
@@ -84,7 +84,7 @@ public function testFragment()
         $this->assertTrue($fragment->isUsed());
     }
 
-    public function testFragmentReference()
+    public function testFragmentReference(): void
     {
         $reference = new FragmentReference('shipInfo', new Location(1,1));
 
@@ -94,7 +94,7 @@ public function testFragmentReference()
         $this->assertEquals('largeShipInfo', $reference->getName());
     }
 
-    public function testTypedFragmentReference()
+    public function testTypedFragmentReference(): void
     {
         $fields = [
             new Field('id', null, [], [], new Location(1,1))
@@ -117,7 +117,7 @@ public function testTypedFragmentReference()
         $this->assertEquals($newFields, $reference->getFields());
     }
 
-    public function testQuery()
+    public function testQuery(): void
     {
         $arguments = [
             new Argument('limit', new Literal('10', new Location(1,1)), new Location(1,1))
@@ -151,7 +151,7 @@ public function testQuery()
         $this->assertTrue($query->hasArguments());
     }
 
-    public function testArgumentValues()
+    public function testArgumentValues(): void
     {
         $list = new InputList(['a', 'b'], new Location(1,1));
         $this->assertEquals(['a', 'b'], $list->getValue());
@@ -169,7 +169,7 @@ public function testArgumentValues()
         $this->assertEquals('new text', $literal->getValue());
     }
 
-    public function testVariable()
+    public function testVariable(): void
     {
         $variable = new Variable('id', 'int', false, false, true, new Location(1,1));
 
@@ -197,7 +197,7 @@ public function testVariable()
     /**
      * @expectedException \LogicException
      */
-    public function testVariableLogicException()
+    public function testVariableLogicException(): void
     {
         $variable = new Variable('id', 'int', false, false, true, new Location(1,1));
         $variable->getValue();
diff --git a/tests/Parser/ParserTest.php b/tests/Parser/ParserTest.php
index 0263d169..1a1a2b06 100644
--- a/tests/Parser/ParserTest.php
+++ b/tests/Parser/ParserTest.php
@@ -24,7 +24,7 @@
 use Youshido\GraphQL\Parser\Token;
 
 class TokenizerTestingParser extends Parser {
-    public function initTokenizerForTesting($source) {
+    public function initTokenizerForTesting($source): void {
         $this->initTokenizer($source);
     }
 
@@ -36,7 +36,7 @@ public function getTokenForTesting() {
 class ParserTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testEmptyParser()
+    public function testEmptyParser(): void
     {
         $parser = new Parser();
 
@@ -53,10 +53,10 @@ public function testEmptyParser()
     /**
      * @expectedException Youshido\GraphQL\Exception\Parser\SyntaxErrorException
      */
-    public function testInvalidSelection()
+    public function testInvalidSelection(): void
     {
         $parser = new Parser();
-        $data   = $parser->parse('
+        $parser->parse('
         {
             test {
                 id
@@ -68,7 +68,7 @@ public function testInvalidSelection()
         ');
     }
 
-    public function testComments()
+    public function testComments(): void
     {
         $query = <<<GRAPHQL
 # asdasd "asdasdasd"
@@ -102,7 +102,7 @@ public function testComments()
         ]);
     }
 
-    private function tokenizeStringContents($graphQLString) {
+    private function tokenizeStringContents(string $graphQLString) {
         $parser = new TokenizerTestingParser();
         $parser->initTokenizerForTesting('"' . $graphQLString . '"');
 
@@ -110,7 +110,7 @@ private function tokenizeStringContents($graphQLString) {
     }
 
 
-    public function testEscapedStrings()
+    public function testEscapedStrings(): void
     {
         $this->assertEquals([
                 $this->tokenizeStringContents(""),           
@@ -143,14 +143,14 @@ public function testEscapedStrings()
      * @dataProvider wrongQueriesProvider
      * @expectedException Youshido\GraphQL\Exception\Parser\SyntaxErrorException
      */
-    public function testWrongQueries($query)
+    public function testWrongQueries($query): void
     {
         $parser = new Parser();
 
         $parser->parse($query);
     }
 
-    public function testCommas()
+    public function testCommas(): void
     {
         $parser = new Parser();
         $data   = $parser->parse('{ foo,       ,,  , bar  }');
@@ -160,7 +160,7 @@ public function testCommas()
         ], $data['queries']);
     }
 
-    public function testQueryWithNoFields()
+    public function testQueryWithNoFields(): void
     {
         $parser = new Parser();
         $data   = $parser->parse('{ name }');
@@ -176,7 +176,7 @@ public function testQueryWithNoFields()
         ], $data);
     }
 
-    public function testQueryWithFields()
+    public function testQueryWithFields(): void
     {
         $parser = new Parser();
         $data   = $parser->parse('{ post, user { name } }');
@@ -195,7 +195,7 @@ public function testQueryWithFields()
         ], $data);
     }
 
-    public function testFragmentWithFields()
+    public function testFragmentWithFields(): void
     {
         $parser = new Parser();
         $data   = $parser->parse('
@@ -222,7 +222,7 @@ public function testFragmentWithFields()
         ], $data);
     }
 
-    public function testInspectionQuery()
+    public function testInspectionQuery(): void
     {
         $parser = new Parser();
 
@@ -422,7 +422,7 @@ public function wrongQueriesProvider()
     /**
      * @dataProvider mutationProvider
      */
-    public function testMutations($query, $structure)
+    public function testMutations($query, $structure): void
     {
         $parser = new Parser();
 
@@ -431,7 +431,7 @@ public function testMutations($query, $structure)
         $this->assertEquals($parsedStructure, $structure);
     }
 
-    public function testTypedFragment()
+    public function testTypedFragment(): void
     {
         $parser          = new Parser();
         $parsedStructure = $parser->parse('
@@ -553,7 +553,7 @@ public function mutationProvider()
     /**
      * @dataProvider queryProvider
      */
-    public function testParser($query, $structure)
+    public function testParser($query, $structure): void
     {
         $parser          = new Parser();
         $parsedStructure = $parser->parse($query);
@@ -831,7 +831,7 @@ public function queryProvider()
         ];
     }
 
-    public function testVariablesInQuery()
+    public function testVariablesInQuery(): void
     {
         $parser = new Parser();
 
@@ -874,7 +874,7 @@ public function testVariablesInQuery()
         $this->assertArrayNotHasKey('errors', $data);
     }
 
-    public function testVariableDefaultValue()
+    public function testVariableDefaultValue(): void
     {
         // Test with non-null default value
         $parser          = new Parser();
diff --git a/tests/Parser/RequestTest.php b/tests/Parser/RequestTest.php
index 49409484..551b40c1 100644
--- a/tests/Parser/RequestTest.php
+++ b/tests/Parser/RequestTest.php
@@ -16,7 +16,7 @@
 class RequestTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testMethods()
+    public function testMethods(): void
     {
         $fragment1     = new Fragment('fragmentName1', 'test', [], [], new Location(1,1));
         $fragment2     = new Fragment('fragmentName2', 'test', [], [], new Location(1,1));
@@ -51,7 +51,7 @@ public function testMethods()
         $this->assertNull($request->getFragment('unknown fragment'));
     }
 
-    public function testSetVariableParseJson()
+    public function testSetVariableParseJson(): void
     {
         $variables = '{"foo": "bar"}';
         $expectedVariableArray = [ 'foo' => 'bar' ];
diff --git a/tests/Parser/VariableTest.php b/tests/Parser/VariableTest.php
index 5ff0da38..04e802e2 100644
--- a/tests/Parser/VariableTest.php
+++ b/tests/Parser/VariableTest.php
@@ -12,7 +12,7 @@ class VariableTest extends \PHPUnit_Framework_TestCase
      *
      * @dataProvider variableProvider
      */
-    public function testGetValue($actual, $expected)
+    public function testGetValue($actual, $expected): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
         $var->setValue($actual);
@@ -23,13 +23,13 @@ public function testGetValue($actual, $expected)
      * @expectedException \LogicException
      * @expectedExceptionMessage Value is not set for variable "foo"
      */
-    public function testGetNullValueException()
+    public function testGetNullValueException(): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
         $var->getValue();
     }
 
-    public function testGetValueReturnsDefaultValueIfNoValueSet()
+    public function testGetValueReturnsDefaultValueIfNoValueSet(): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
         $var->setDefaultValue('default-value');
@@ -40,7 +40,7 @@ public function testGetValueReturnsDefaultValueIfNoValueSet()
         );
     }
 
-    public function testGetValueReturnsSetValueEvenWithDefaultValue()
+    public function testGetValueReturnsSetValueEvenWithDefaultValue(): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
         $var->setValue('real-value');
@@ -52,7 +52,7 @@ public function testGetValueReturnsSetValueEvenWithDefaultValue()
         );
     }
 
-    public function testIndicatesDefaultValuePresent()
+    public function testIndicatesDefaultValuePresent(): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
         $var->setDefaultValue('default-value');
@@ -62,7 +62,7 @@ public function testIndicatesDefaultValuePresent()
         );
     }
 
-    public function testHasNoDefaultValue()
+    public function testHasNoDefaultValue(): void
     {
         $var = new Variable('foo', 'bar', false, false, true, new Location(1,1));
 
diff --git a/tests/Performance/LoadTest.php b/tests/Performance/LoadTest.php
index e110f93c..595a699a 100644
--- a/tests/Performance/LoadTest.php
+++ b/tests/Performance/LoadTest.php
@@ -19,9 +19,9 @@
 class LoadTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testLoad10k()
+    public function testLoad10k(): bool
     {
-        $time = microtime(true);
+        microtime(true);
         $postType = new ObjectType([
             'name'   => 'Post',
             'fields' => [
@@ -46,6 +46,7 @@ public function testLoad10k()
                     'name' => 'Author ' . substr(md5(time()), 0, 4)
                 ];
             }
+            
             $data[] = [
                 'id'      => $i,
                 'title'   => 'Title of ' . $i,
@@ -53,13 +54,13 @@ public function testLoad10k()
             ];
         }
 
-        $p = new Processor(new Schema([
+        new Processor(new Schema([
             'query' => new ObjectType([
                 'name' => 'RootQuery',
                 'fields' => [
                     'posts' => [
                         'type' => new ListType($postType),
-                        'resolve' => function() use ($data) {
+                        'resolve' => static function () use ($data) {
                             return $data;
                         }
                     ]
@@ -67,11 +68,6 @@ public function testLoad10k()
             ]),
         ]));
         return true;
-        $p->processPayload('{ posts { id, title, authors { name } } }');
-        $res = $p->getResponseData();
-        echo "Count: " . count($res['data']['posts']) . "\n";
-        var_dump($res['data']['posts'][0]);
-        printf("Test Time: %04f\n", microtime(true) - $time);
     }
 
 }
\ No newline at end of file
diff --git a/tests/Performance/NPlusOneTest.php b/tests/Performance/NPlusOneTest.php
index 5832d331..9e4093cd 100644
--- a/tests/Performance/NPlusOneTest.php
+++ b/tests/Performance/NPlusOneTest.php
@@ -32,7 +32,7 @@ private function getDataForPosts()
             ['id' => 3, 'name' => 'Mike'],
         ];
         $posts   = [];
-        for ($i = 0; $i < 10; $i++) {
+        for ($i = 0; $i < 10; ++$i) {
             $posts[] = [
                 'id'     => $i + 1,
                 'title'  => sprintf('Post title $%s', $i),
@@ -43,7 +43,7 @@ private function getDataForPosts()
         return $posts;
     }
 
-    public function testHigherResolver()
+    public function testHigherResolver(): void
     {
         $authorType = new ObjectType([
             'name'   => 'Author',
diff --git a/tests/Schema/DeferredTest.php b/tests/Schema/DeferredTest.php
index a1eb764d..ef8679ee 100644
--- a/tests/Schema/DeferredTest.php
+++ b/tests/Schema/DeferredTest.php
@@ -8,6 +8,7 @@
 
 namespace Youshido\Tests\Schema;
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Config\Schema\SchemaConfig;
 use Youshido\GraphQL\Execution\DeferredResolver;
 use Youshido\GraphQL\Execution\Processor;
@@ -42,7 +43,7 @@ public function query(array $ids);
 class DeferredQueryBuffer
 {
 
-    protected $database;
+    protected \Youshido\Tests\Schema\DeferredDatabase $database;
 
     protected $buffer = [];
 
@@ -75,6 +76,7 @@ protected function fetch($resultId)
                 foreach ($query as $id) {
                     $this->results[$index][$id] = $result[$id];
                 }
+                
                 unset($this->buffer[$index]);
             }
         }
@@ -86,10 +88,7 @@ protected function fetch($resultId)
 class DeferredUserType extends AbstractObjectType
 {
 
-    /**
-     * @var \Youshido\Tests\Schema\DeferredQueryBuffer
-     */
-    protected $database;
+    protected \Youshido\Tests\Schema\DeferredQueryBuffer $database;
 
     public function __construct(DeferredQueryBuffer $database)
     {
@@ -98,14 +97,14 @@ public function __construct(DeferredQueryBuffer $database)
     }
 
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addField(
           new Field(
             [
               'name' => 'name',
               'type' => new StringType(),
-              'resolve' => function ($value) {
+              'resolve' => static function (array $value) {
                   return $value['name'];
               },
             ]
@@ -117,7 +116,7 @@ public function build($config)
             [
               'name' => 'friends',
               'type' => new ListType(new DeferredUserType($this->database)),
-              'resolve' => function ($value) {
+              'resolve' => function (array $value): \Youshido\GraphQL\Execution\DeferredResolver {
                   return new DeferredResolver(
                     $this->database->add($value['friends'])
                   );
@@ -131,7 +130,7 @@ public function build($config)
             [
               'name' => 'foes',
               'type' => new ListType(new DeferredUserType($this->database)),
-              'resolve' => function ($value) {
+              'resolve' => function (array $value): \Youshido\GraphQL\Execution\DeferredResolver {
                   return new DeferredResolver(
                     $this->database->add($value['foes'])
                   );
@@ -151,7 +150,7 @@ public function __construct(DeferredQueryBuffer $buffer)
           [
             'name' => 'users',
             'type' => new ListType(new DeferredUserType($buffer)),
-            'resolve' => function ($value, $args) use ($buffer) {
+            'resolve' => static function ($value, array $args) use ($buffer) : \Youshido\GraphQL\Execution\DeferredResolver {
                 return new DeferredResolver($buffer->add($args['ids']));
             },
           ]
@@ -176,7 +175,7 @@ public function __construct(DeferredQueryBuffer $buffer)
     }
 
 
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
     }
 
@@ -206,7 +205,7 @@ protected function query($query, DeferredQueryBuffer $buffer)
     /**
      * Test a simple single deferred field.
      */
-    public function testSingleResolve()
+    public function testSingleResolve(): void
     {
         $query = 'query {
           users(ids: ["a", "b"]) {
@@ -244,7 +243,7 @@ public function testSingleResolve()
     /**
      * Test if multiple calls to the same field result in a single query.
      */
-    public function testMultiResolve()
+    public function testMultiResolve(): void
     {
 
         $query = 'query {
@@ -290,7 +289,7 @@ public function testMultiResolve()
     /**
      * Test if recursive deferred resolvers work properly.
      */
-    public function testRecursiveResolve()
+    public function testRecursiveResolve(): void
     {
 
         $query = 'query {
@@ -344,7 +343,7 @@ public function testRecursiveResolve()
     /**
      * Test if multiple deferred resolvers are optimized into two queries.
      */
-    public function testMultiRecursiveResolve()
+    public function testMultiRecursiveResolve(): void
     {
 
         $query = 'query {
diff --git a/tests/Schema/FragmentsTest.php b/tests/Schema/FragmentsTest.php
index 72bcbd7b..e881ddd6 100644
--- a/tests/Schema/FragmentsTest.php
+++ b/tests/Schema/FragmentsTest.php
@@ -19,7 +19,7 @@
 
 class UserType extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addFields([
             'id'           => new IdType(),
@@ -32,7 +32,7 @@ public function build($config)
 class CourtReservation extends AbstractObjectType
 {
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addFields([
             'id'      => new IdType(),
@@ -46,7 +46,7 @@ public function build($config)
         ]);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new ReservationInterface()];
     }
@@ -55,7 +55,7 @@ public function getInterfaces()
 
 class ClassReservation extends AbstractObjectType
 {
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config->addFields([
             'id'   => new IdType(),
@@ -63,7 +63,7 @@ public function build($config)
         ]);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new ReservationInterface()];
     }
@@ -71,12 +71,12 @@ public function getInterfaces()
 
 class ReservationInterface extends AbstractInterfaceType
 {
-    public function resolveType($object)
+    public function resolveType($object): \Youshido\Tests\Schema\CourtReservation|\Youshido\Tests\Schema\ClassReservation
     {
-        return strpos($object['id'], 'cl') === false ? new CourtReservation() : new ClassReservation();
+        return strpos((string) $object['id'], 'cl') === false ? new CourtReservation() : new ClassReservation();
     }
 
-    public function build($config)
+    public function build(InterfaceTypeConfig $config): void
     {
         $config->addFields([
             'id' => new IdType()
@@ -95,7 +95,7 @@ class FragmentsTest extends \PHPUnit_Framework_TestCase
      * @param $expected
      * @param $variables
      */
-    public function testVariables($query, $expected, $variables)
+    public function testVariables($query, $expected, $variables): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -103,7 +103,7 @@ public function testVariables($query, $expected, $variables)
                 'fields' => [
                     'user' => [
                         'type'    => new UserType(),
-                        'resolve' => function ($args) {
+                        'resolve' => static function ($args) : array {
                             return [
                                 'id'           => 'user-id-1',
                                 'fullName'     => 'Alex',
@@ -137,6 +137,7 @@ public function testVariables($query, $expected, $variables)
 
         $processor = new Processor($schema);
         $processor->processPayload($query, $variables);
+        
         $result = $processor->getResponseData();
 
         $this->assertEquals($expected, $result);
@@ -209,7 +210,7 @@ public function queries()
         ];
     }
 
-    public function testSimpleFragment()
+    public function testSimpleFragment(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -217,7 +218,7 @@ public function testSimpleFragment()
                 'fields' => [
                     'user' => [
                         'type'    => new UserType(),
-                        'resolve' => function ($args) {
+                        'resolve' => static function ($args) : array {
                             return [
                                 'id'       => 'user-id-1',
                                 'fullName' => 'Alex',
@@ -247,6 +248,7 @@ public function testSimpleFragment()
 
         $processor = new Processor($schema);
         $processor->processPayload($query);
+        
         $result = $processor->getResponseData();
 
         $expected = ['data' => ['User1' => ['fullName' => 'Alex'], 'User2' => ['fullName' => 'Alex']]];
diff --git a/tests/Schema/InputObjectDefaultValuesTest.php b/tests/Schema/InputObjectDefaultValuesTest.php
index a13c60d3..61555848 100644
--- a/tests/Schema/InputObjectDefaultValuesTest.php
+++ b/tests/Schema/InputObjectDefaultValuesTest.php
@@ -16,7 +16,7 @@
 class InputObjectDefaultValuesTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testDefaultEnum()
+    public function testDefaultEnum(): void
     {
         $enumType = new EnumType([
             'name'   => 'InternalStatus',
@@ -49,7 +49,7 @@ public function testDefaultEnum()
                                 ]
                             ])
                         ],
-                        'resolve'    => function ($source, $args) {
+                        'resolve'    => static function ($source, array $args) : string {
                             return sprintf('Result with level %s and status %s',
                                 $args['statObject']['level'], $args['statObject']['status']
                             );
@@ -62,7 +62,7 @@ public function testDefaultEnum()
                                 'status' => $enumType
                             ]
                         ]),
-                        'resolve' => function() {
+                        'resolve' => static function () : array {
                             return [
                                 'status' => null
                             ];
@@ -75,6 +75,7 @@ public function testDefaultEnum()
 
         $processor = new Processor($schema);
         $processor->processPayload('{ stringQuery(statObject: { level: 1 }) }');
+        
         $result = $processor->getResponseData();
         $this->assertEquals(['data' => [
             'stringQuery' => 'Result with level 1 and status 1'
diff --git a/tests/Schema/InputParseTest.php b/tests/Schema/InputParseTest.php
index d3bc3b86..2faa325f 100644
--- a/tests/Schema/InputParseTest.php
+++ b/tests/Schema/InputParseTest.php
@@ -18,7 +18,7 @@ class InputParseTest extends \PHPUnit_Framework_TestCase
      * @param $query
      * @param $expected
      */
-    public function testDateInput($query, $expected)
+    public function testDateInput($query, $expected): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -30,7 +30,7 @@ public function testDateInput($query, $expected)
                             'from'   => new DateTimeType('Y-m-d H:i:s'),
                             'fromtz' => new DateTimeTzType(),
                         ],
-                        'resolve' => function ($source, $args) {
+                        'resolve' => static function ($source, array $args) : string {
                             return sprintf('Result with %s date and %s tz',
                                 empty($args['from']) ? 'default' : $args['from']->format('Y-m-d H:i:s'),
                                 empty($args['fromtz']) ? 'default' : $args['fromtz']->format('r')
@@ -43,6 +43,7 @@ public function testDateInput($query, $expected)
 
         $processor = new Processor($schema);
         $processor->processPayload($query);
+        
         $result = $processor->getResponseData();
 
         $this->assertEquals($expected, $result);
diff --git a/tests/Schema/IntrospectionTest.php b/tests/Schema/IntrospectionTest.php
index 7bdafee0..ae25b089 100644
--- a/tests/Schema/IntrospectionTest.php
+++ b/tests/Schema/IntrospectionTest.php
@@ -27,7 +27,7 @@
 
 class IntrospectionTest extends \PHPUnit_Framework_TestCase
 {
-    private $introspectionQuery = <<<TEXT
+    private string $introspectionQuery = <<<TEXT
 query IntrospectionQuery {
                 __schema {
                     queryType { name }
@@ -105,7 +105,7 @@ enumValues {
 TEXT;
 
 
-    public function testIntrospectionDirectiveRequest()
+    public function testIntrospectionDirectiveRequest(): void
     {
         $processor = new Processor(new TestSchema());
 
@@ -120,7 +120,7 @@ public function testIntrospectionDirectiveRequest()
      *
      * @dataProvider predefinedSchemaProvider
      */
-    public function testPredefinedQueries($query, $expectedResponse)
+    public function testPredefinedQueries($query, $expectedResponse): void
     {
         $schema = new TestEmptySchema();
         $schema->addQueryField(new Field([
@@ -139,7 +139,7 @@ public function testPredefinedQueries($query, $expectedResponse)
             'description'       => 'latest description',
             'deprecationReason' => 'for test',
             'isDeprecated'      => true,
-            'resolve'           => function () {
+            'resolve'           => static function () : array {
                 return [
                     'id'   => 1,
                     'name' => 'Alex'
@@ -150,6 +150,7 @@ public function testPredefinedQueries($query, $expectedResponse)
         $processor = new Processor($schema);
 
         $processor->processPayload($query);
+        
         $responseData = $processor->getResponseData();
 
         $this->assertEquals($expectedResponse, $responseData);
@@ -285,7 +286,7 @@ interfaces {
         ];
     }
 
-    public function testCombinedFields()
+    public function testCombinedFields(): void
     {
         $schema = new TestEmptySchema();
 
@@ -295,8 +296,7 @@ public function testCombinedFields()
                 'id'   => ['type' => new IntType()],
                 'name' => ['type' => new IntType()],
             ],
-            'resolveType' => function ($type) {
-
+            'resolveType' => static function ($type) : void {
             }
         ]);
 
@@ -323,8 +323,7 @@ public function testCombinedFields()
         $unionType = new UnionType([
             'name'        => 'UnionType',
             'types'       => [$object1, $object2],
-            'resolveType' => function () {
-
+            'resolveType' => static function () : void {
             }
         ]);
 
@@ -334,7 +333,7 @@ public function testCombinedFields()
             'args'    => [
                 'id' => ['type' => TypeMap::TYPE_INT]
             ],
-            'resolve' => function () {
+            'resolve' => static function () : array {
                 return [
                     'id'   => 1,
                     'name' => 'Alex'
@@ -360,7 +359,7 @@ public function testCombinedFields()
                     ]
                 ])
             ],
-            'resolve' => function () {
+            'resolve' => static function () {
                 return null;
             }
         ]));
@@ -368,13 +367,14 @@ public function testCombinedFields()
         $processor = new Processor($schema);
 
         $processor->processPayload($this->introspectionQuery);
+        
         $responseData = $processor->getResponseData();
 
         /** strange that this test got broken after I fixed the field resolve behavior */
         $this->assertArrayNotHasKey('errors', $responseData);
     }
 
-    public function testCanIntrospectDirectives()
+    public function testCanIntrospectDirectives(): void
     {
         $schema = new TestSchema();
         $schema->getDirectiveList()->addDirectives([
@@ -429,6 +429,7 @@ public function testCanIntrospectDirectives()
         $processor = new Processor($schema);
 
         $processor->processPayload($this->introspectionQuery);
+        
         $responseData = $processor->getResponseData();
         $this->assertArrayNotHasKey('errors', $responseData);
     }
diff --git a/tests/Schema/NonNullableTest.php b/tests/Schema/NonNullableTest.php
index 8069cc35..35f09d7e 100644
--- a/tests/Schema/NonNullableTest.php
+++ b/tests/Schema/NonNullableTest.php
@@ -18,14 +18,14 @@
 
 class uid
 {
-    private $uid;
+    private readonly string $uid;
 
     public function __construct($uid)
     {
         $this->uid = $uid;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->uid;
     }
@@ -40,7 +40,7 @@ class NonNullableTest extends \PHPUnit_Framework_TestCase
      * @param $query
      * @param $expected
      */
-    public function testNullableResolving($query, $expected)
+    public function testNullableResolving($query, $expected): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -48,13 +48,13 @@ public function testNullableResolving($query, $expected)
                 'fields' => [
                     'nonNullScalar'        => [
                         'type'    => new NonNullType(new IntType()),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         },
                     ],
                     'nonNullList'          => [
                         'type'    => new NonNullType(new ListType(new IntType())),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ],
@@ -66,7 +66,7 @@ public function testNullableResolving($query, $expected)
                                 'name' => new StringType(),
                             ]
                         ])),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 'id'   => new uid('6cfb044c-9c0a-4ddd-9ef8-a0b940818db3'),
                                 'name' => 'Alex'
@@ -75,7 +75,7 @@ public function testNullableResolving($query, $expected)
                     ],
                     'nonNullListOfNpnNull' => [
                         'type'    => new NonNullType(new ListType(new NonNullType(new IntType()))),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [1, null];
                         }
                     ],
@@ -84,7 +84,7 @@ public function testNullableResolving($query, $expected)
                             'ids' => new NonNullType(new ListType(new IntType()))
                         ],
                         'type'    => new IntType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : int {
                             return 1;
                         }
                     ],
@@ -93,7 +93,7 @@ public function testNullableResolving($query, $expected)
                             'ids' => new NonNullType(new ListType(new NonNullType(new IntType())))
                         ],
                         'type'    => new IntType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : int {
                             return 1;
                         }
                     ],
@@ -103,6 +103,7 @@ public function testNullableResolving($query, $expected)
 
         $processor = new Processor($schema);
         $processor->processPayload($query);
+        
         $result = $processor->getResponseData();
 
         $this->assertEquals($expected, $result);
diff --git a/tests/Schema/ProcessorTest.php b/tests/Schema/ProcessorTest.php
index 545416c7..6a7ae05e 100644
--- a/tests/Schema/ProcessorTest.php
+++ b/tests/Schema/ProcessorTest.php
@@ -34,15 +34,15 @@
 class ProcessorTest extends \PHPUnit_Framework_TestCase
 {
 
-    private $_counter = 0;
+    private int $_counter = 0;
 
-    public function testInit()
+    public function testInit(): void
     {
         $processor = new Processor(new TestEmptySchema());
         $this->assertEquals([['message' => 'Schema has to have fields']], $processor->getExecutionContext()->getErrorsArray());
     }
 
-    public function testEmptyQueries()
+    public function testEmptyQueries(): void
     {
         $processor = new Processor(new TestSchema());
         $processor->processPayload('');
@@ -58,7 +58,7 @@ public function testEmptyQueries()
 
     }
 
-    public function testNestedVariables()
+    public function testNestedVariables(): void
     {
         $processor    = new Processor(new TestSchema());
         $noArgsQuery  = '{ me { echo(value:"foo") } }';
@@ -88,7 +88,7 @@ public function testNestedVariables()
         $this->assertArrayNotHasKey('errors', $processor->getResponseData());
     }
 
-    public function testNullListVariable()
+    public function testNullListVariable(): void
     {
         $processor = new Processor(new TestSchema());
         $processor->processPayload(
@@ -102,7 +102,7 @@ public function testNullListVariable()
         $this->assertArrayNotHasKey('errors', $processor->getResponseData());
     }
 
-    public function testListNullResponse()
+    public function testListNullResponse(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -110,7 +110,7 @@ public function testListNullResponse()
                 'fields' => [
                     'list' => [
                         'type'    => new ListType(new StringType()),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ]
@@ -122,7 +122,7 @@ public function testListNullResponse()
     }
 
 
-    public function testSubscriptionNullResponse()
+    public function testSubscriptionNullResponse(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -130,7 +130,7 @@ public function testSubscriptionNullResponse()
                 'fields' => [
                     'list' => [
                         'type'    => new ListType(new StringType()),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ]
@@ -141,7 +141,7 @@ public function testSubscriptionNullResponse()
         $this->assertEquals(['data' => ['__schema' => ['subscriptionType' => null]]], $data);
     }
 
-    public function testSchemaOperations()
+    public function testSchemaOperations(): void
     {
         $schema    = new Schema([
             'query' => new ObjectType([
@@ -156,13 +156,13 @@ public function testSchemaOperations()
                                     'args'    => [
                                         'shorten' => new BooleanType()
                                     ],
-                                    'resolve' => function ($value, $args) {
+                                    'resolve' => static function (array $value, array $args) {
                                         return empty($args['shorten']) ? $value['firstName'] : $value['firstName'];
                                     }
                                 ],
                                 'id_alias'  => [
                                     'type'    => new IdType(),
-                                    'resolve' => function ($value) {
+                                    'resolve' => static function (array $value) {
                                         return $value['id'];
                                     }
                                 ],
@@ -170,14 +170,13 @@ public function testSchemaOperations()
                                 'code'      => new StringType(),
                             ]
                         ]),
-                        'resolve' => function ($value, $args) {
+                        'resolve' => static function ($value, array $args) : array {
                             $data = ['id' => '123', 'firstName' => 'John', 'code' => '007'];
                             if (!empty($args['upper'])) {
                                 foreach ($data as $key => $value) {
                                     $data[$key] = strtoupper($value);
                                 }
                             }
-
                             return $data;
                         },
                         'args'    => [
@@ -189,19 +188,19 @@ public function testSchemaOperations()
                     ],
                     'randomUser'        => [
                         'type'    => new TestObjectType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return ['invalidField' => 'John'];
                         }
                     ],
                     'invalidValueQuery' => [
                         'type'    => new TestObjectType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'stringValue';
                         }
                     ],
                     'labels'            => [
                         'type'    => new ListType(new StringType()),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return ['one', 'two'];
                         }
                     ]
@@ -238,7 +237,7 @@ public function testSchemaOperations()
             ->addField(new Field([
                 'name'    => 'increaseCounter',
                 'type'    => new IntType(),
-                'resolve' => function ($value, $args, ResolveInfo $info) {
+                'resolve' => function ($value, array $args, ResolveInfo $info): float|int|array {
                     return $this->_counter += $args['amount'];
                 },
                 'args'    => [
@@ -250,13 +249,13 @@ public function testSchemaOperations()
             ]))->addField(new Field([
                 'name'    => 'invalidResolveTypeMutation',
                 'type'    => new NonNullType(new IntType()),
-                'resolve' => function () {
+                'resolve' => static function () {
                     return null;
                 }
             ]))->addField(new Field([
                 'name'    => 'interfacedMutation',
                 'type'    => new TestInterfaceType(),
-                'resolve' => function () {
+                'resolve' => static function () : array {
                     return ['name' => 'John'];
                 }
             ]));
@@ -362,7 +361,7 @@ public function testSchemaOperations()
         $this->assertEquals(['data' => ['user' => ['name' => 'John']]], $processor->getResponseData());
     }
 
-    public function testEnumType()
+    public function testEnumType(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -385,7 +384,7 @@ public function testEnumType()
                             ]))
                         ],
                         'type'    => new StringType(),
-                        'resolve' => function ($value, $args) {
+                        'resolve' => static function ($value, array $args) {
                             return $args['argument1'];
                         }
                     ]
@@ -394,6 +393,7 @@ public function testEnumType()
         ]));
 
         $processor->processPayload('{ test }');
+        
         $response = $processor->getResponseData();
         $this->assertEquals([
             'data'   => ['test' => null],
@@ -430,7 +430,7 @@ public function testEnumType()
         $this->assertEquals(['data' => ['alias' => 'val1']], $response);
     }
 
-    public function testListEnumsSchemaOperations()
+    public function testListEnumsSchemaOperations(): void
     {
         $processor = new Processor(new Schema([
             'query' => new ObjectType([
@@ -438,43 +438,43 @@ public function testListEnumsSchemaOperations()
                 'fields' => [
                     'listQuery'                 => [
                         'type'    => new ListType(new TestEnumType()),
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'invalid list';
                         }
                     ],
                     'listEnumQuery'             => [
                         'type'    => new ListType(new TestEnumType()),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return ['invalid enum'];
                         }
                     ],
                     'invalidEnumQuery'          => [
                         'type'    => new TestEnumType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'invalid enum';
                         }
                     ],
                     'enumQuery'                 => [
                         'type'    => new TestEnumType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : int {
                             return 1;
                         }
                     ],
                     'invalidNonNullQuery'       => [
                         'type'    => new NonNullType(new IntType()),
-                        'resolve' => function () {
+                        'resolve' => static function () {
                             return null;
                         }
                     ],
                     'invalidNonNullInsideQuery' => [
                         'type'    => new NonNullType(new IntType()),
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'hello';
                         }
                     ],
                     'objectQuery'               => [
                         'type'    => new TestObjectType(),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return ['name' => 'John'];
                         }
                     ],
@@ -486,7 +486,7 @@ public function testListEnumsSchemaOperations()
                                 'enum'   => new TestEnumType(),
                             ],
                         ]),
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 'object' => [
                                     'name' => 'John'
@@ -541,7 +541,7 @@ public function testListEnumsSchemaOperations()
         $this->assertEquals(['data' => ['test' => ['object' => ['name' => 'John']]]], $processor->getResponseData());
     }
 
-    public function testTypedFragment()
+    public function testTypedFragment(): void
     {
 
         $object1 = new ObjectType([
@@ -568,18 +568,17 @@ public function testTypedFragment()
         $union        = new UnionType([
             'name'        => 'TestUnion',
             'types'       => [$object1, $object2],
-            'resolveType' => function ($object) use ($object1, $object2) {
+            'resolveType' => static function (array $object) use ($object1, $object2) {
                 if (isset($object['id'])) {
                     return $object1;
                 }
-
                 return $object2;
             }
         ]);
         $invalidUnion = new UnionType([
             'name'        => 'TestUnion',
             'types'       => [$object1, $object2],
-            'resolveType' => function ($object) use ($object3) {
+            'resolveType' => static function ($object) use ($object3) {
                 return $object3;
             }
         ]);
@@ -593,7 +592,7 @@ public function testTypedFragment()
                             'type' => ['type' => 'string']
                         ],
                         'cost'    => 10,
-                        'resolve' => function ($value, $args) {
+                        'resolve' => static function ($value, array $args) {
                             if ($args['type'] == 'object1') {
                                 return [
                                     'id' => 43
@@ -607,7 +606,7 @@ public function testTypedFragment()
                     ],
                     'invalidUnion' => [
                         'type'    => $invalidUnion,
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return ['name' => 'name resolved'];
                         }
                     ],
@@ -666,7 +665,7 @@ public function testTypedFragment()
         $this->assertEquals(10 + 13 + 1, $visitor->getMemo());
     }
 
-    public function testContainer()
+    public function testContainer(): void
     {
         $container = new Container();
         $container->set('user', ['name' => 'Alex']);
@@ -677,7 +676,7 @@ public function testContainer()
                 'fields' => [
                     'currentUser' => [
                         'type'    => new StringType(),
-                        'resolve' => function ($source, $args, ResolveInfo $info) {
+                        'resolve' => static function ($source, $args, ResolveInfo $info) {
                             return $info->getContainer()->get('user')['name'];
                         }
                     ]
@@ -692,7 +691,7 @@ public function testContainer()
         $this->assertEquals(['data' => ['currentUser' => 'Alex']], $processor->processPayload('{ currentUser }')->getResponseData());
     }
 
-    public function testComplexityReducer()
+    public function testComplexityReducer(): void
     {
         $schema    = new Schema(
             [
@@ -710,7 +709,7 @@ public function testComplexityReducer()
                                                 'args'    => [
                                                     'shorten' => new BooleanType()
                                                 ],
-                                                'resolve' => function ($value, $args) {
+                                                'resolve' => static function (array $value, array $args) {
                                                     return empty($args['shorten']) ? $value['firstName'] : $value['firstName'];
                                                 }
                                             ],
@@ -719,22 +718,19 @@ public function testComplexityReducer()
                                             'likes'     => [
                                                 'type'    => new IntType(),
                                                 'cost'    => 10,
-                                                'resolve' => function () {
+                                                'resolve' => static function () : int {
                                                     return 42;
                                                 }
                                             ]
                                         ]
                                     ]
                                 ),
-                                'cost'    => function ($args, $context, $childCost) {
+                                'cost'    => static function (array $args, $context, $childCost) : int|float {
                                     $argsCost = isset($args['cost']) ? $args['cost'] : 1;
-
                                     return 1 + $argsCost * $childCost;
                                 },
-                                'resolve' => function ($value, $args) {
-                                    $data = ['firstName' => 'John', 'code' => '007'];
-
-                                    return $data;
+                                'resolve' => static function ($value, $args) : array {
+                                    return ['firstName' => 'John', 'code' => '007'];
                                 },
                                 'args'    => [
                                     'cost' => [
@@ -779,7 +775,7 @@ public function testComplexityReducer()
 
         foreach (range(1, 5) as $cost_multiplier) {
             $visitor = new MaxComplexityQueryVisitor(1000); // arbitrarily high cost
-            $processor->processPayload("{ me (cost: $cost_multiplier) { firstName, lastName, code, likes } }", ['cost' => $cost_multiplier], [$visitor]);
+            $processor->processPayload(sprintf('{ me (cost: %s) { firstName, lastName, code, likes } }', $cost_multiplier), ['cost' => $cost_multiplier], [$visitor]);
             $expected = 1 + 13 * (1 + $cost_multiplier);
             $this->assertEquals($expected, $visitor->getMemo());
         }
diff --git a/tests/Schema/ResolveInfoTest.php b/tests/Schema/ResolveInfoTest.php
index af903980..e3bad06d 100644
--- a/tests/Schema/ResolveInfoTest.php
+++ b/tests/Schema/ResolveInfoTest.php
@@ -19,7 +19,7 @@
 
 class ResolveInfoTest extends \PHPUnit_Framework_TestCase
 {
-    public function testMethods()
+    public function testMethods(): void
     {
         $fieldAst         = new FieldAST('name', null, [], [], new Location(1,1));
         $field            = new Field(['name' => 'id', 'type' => new IntType()]);
diff --git a/tests/Schema/SchemaTest.php b/tests/Schema/SchemaTest.php
index 5c1c75fe..a21f558e 100644
--- a/tests/Schema/SchemaTest.php
+++ b/tests/Schema/SchemaTest.php
@@ -22,13 +22,13 @@
 class SchemaTest extends \PHPUnit_Framework_TestCase
 {
 
-    public function testStandaloneEmptySchema()
+    public function testStandaloneEmptySchema(): void
     {
         $schema = new TestEmptySchema();
         $this->assertFalse($schema->getQueryType()->hasFields());
     }
 
-    public function testStandaloneSchema()
+    public function testStandaloneSchema(): void
     {
         $schema = new TestSchema();
         $this->assertTrue($schema->getQueryType()->hasFields());
@@ -36,13 +36,13 @@ public function testStandaloneSchema()
 
         $this->assertEquals(1, count($schema->getMutationType()->getFields()));
 
-        $schema->addMutationField('changeUser', ['type' => new TestObjectType(), 'resolve' => function () {
+        $schema->addMutationField('changeUser', ['type' => new TestObjectType(), 'resolve' => static function () : void {
         }]);
         $this->assertEquals(2, count($schema->getMutationType()->getFields()));
 
     }
 
-    public function testSchemaWithoutClosuresSerializable()
+    public function testSchemaWithoutClosuresSerializable(): void
     {
         $schema = new TestEmptySchema();
         $schema->getQueryType()->addField('randomInt', [
@@ -59,7 +59,7 @@ public function testSchemaWithoutClosuresSerializable()
         $this->assertEquals(1, count($unserialized->getQueryType()->getFields()));
     }
 
-    public function testCustomTypes()
+    public function testCustomTypes(): void
     {
         $authorType = null;
 
@@ -68,7 +68,7 @@ public function testCustomTypes()
             'fields'      => [
                 'name' => new StringType(),
             ],
-            'resolveType' => function () use ($authorType) {
+            'resolveType' => static function () use ($authorType) {
                 return $authorType;
             }
         ]);
@@ -87,7 +87,7 @@ public function testCustomTypes()
                 'fields' => [
                     'user' => [
                         'type'    => $userInterface,
-                        'resolve' => function () {
+                        'resolve' => static function () : array {
                             return [
                                 'name' => 'Alex'
                             ];
diff --git a/tests/Schema/VariablesTest.php b/tests/Schema/VariablesTest.php
index c04ab334..9e613dc2 100644
--- a/tests/Schema/VariablesTest.php
+++ b/tests/Schema/VariablesTest.php
@@ -12,7 +12,7 @@
 
 class VariablesTest extends \PHPUnit_Framework_TestCase
 {
-    public function testInvalidNullableList()
+    public function testInvalidNullableList(): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -23,7 +23,7 @@ public function testInvalidNullableList()
                         'args'    => [
                             'ids' => new ListType(new NonNullType(new IdType())),
                         ],
-                        'resolve' => function () {
+                        'resolve' => static function () : string {
                             return 'item';
                         },
                     ],
@@ -89,7 +89,7 @@ public function testInvalidNullableList()
      * @param $expected
      * @param $variables
      */
-    public function testVariables($query, $expected, $variables)
+    public function testVariables($query, $expected, $variables): void
     {
         $schema = new Schema([
             'query' => new ObjectType([
@@ -100,7 +100,7 @@ public function testVariables($query, $expected, $variables)
                         'args'    => [
                             'sortOrder' => new StringType(),
                         ],
-                        'resolve' => function ($args) {
+                        'resolve' => static function (array $args) : string {
                             return sprintf('Result with %s order', empty($args['sortOrder']) ? 'default' : $args['sortOrder']);
                         },
                     ],
@@ -110,6 +110,7 @@ public function testVariables($query, $expected, $variables)
 
         $processor = new Processor($schema);
         $processor->processPayload($query, $variables);
+        
         $result = $processor->getResponseData();
 
         $this->assertEquals($expected, $result);
diff --git a/tests/StarWars/Schema/CharacterInterface.php b/tests/StarWars/Schema/CharacterInterface.php
index 273aaf14..97627231 100644
--- a/tests/StarWars/Schema/CharacterInterface.php
+++ b/tests/StarWars/Schema/CharacterInterface.php
@@ -8,6 +8,7 @@
 
 namespace Youshido\Tests\StarWars\Schema;
 
+use Youshido\GraphQL\Config\Object\InterfaceTypeConfig;
 use Youshido\GraphQL\Type\InterfaceType\AbstractInterfaceType;
 use Youshido\GraphQL\Type\ListType\ListType;
 use Youshido\GraphQL\Type\NonNullType;
@@ -16,31 +17,31 @@
 
 class CharacterInterface extends AbstractInterfaceType
 {
-    public function build($config)
+    public function build(InterfaceTypeConfig $config): void
     {
         $config
             ->addField('id', new NonNullType(new IdType()))
             ->addField('name', new NonNullType(new StringType()))
             ->addField('friends', [
                 'type'    => new ListType(new CharacterInterface()),
-                'resolve' => function ($value) {
+                'resolve' => static function (array $value) {
                     return $value['friends'];
                 }
             ])
             ->addField('appearsIn', new ListType(new EpisodeEnum()));
     }
 
-    public function getDescription()
+    public function getDescription(): string
     {
         return 'A character in the Star Wars Trilogy';
     }
 
-    public function getName()
+    public function getName(): string
     {
         return 'Character';
     }
 
-    public function resolveType($object)
+    public function resolveType($object): \Youshido\Tests\StarWars\Schema\HumanType|\Youshido\Tests\StarWars\Schema\DroidType|null
     {
         $humans = StarWarsData::humans();
         $droids = StarWarsData::droids();
diff --git a/tests/StarWars/Schema/DroidType.php b/tests/StarWars/Schema/DroidType.php
index 7b4101df..b7a9d6d5 100644
--- a/tests/StarWars/Schema/DroidType.php
+++ b/tests/StarWars/Schema/DroidType.php
@@ -8,6 +8,7 @@
 namespace Youshido\Tests\StarWars\Schema;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\TypeMap;
 
 class DroidType extends HumanType
@@ -16,16 +17,16 @@ class DroidType extends HumanType
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return 'Droid';
     }
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         parent::build($config);
 
-        $config->getField('friends')->getConfig()->set('resolve', function ($droid) {
+        $config->getField('friends')->getConfig()->set('resolve', static function ($droid) {
             return StarWarsData::getFriends($droid);
         });
 
@@ -33,7 +34,7 @@ public function build($config)
             ->addField('primaryFunction', TypeMap::TYPE_STRING);
     }
 
-    public function getInterfaces()
+    public function getInterfaces(): array
     {
         return [new CharacterInterface()];
     }
diff --git a/tests/StarWars/Schema/EpisodeEnum.php b/tests/StarWars/Schema/EpisodeEnum.php
index 2c4c4436..14ff5862 100644
--- a/tests/StarWars/Schema/EpisodeEnum.php
+++ b/tests/StarWars/Schema/EpisodeEnum.php
@@ -13,7 +13,7 @@
 class EpisodeEnum extends AbstractEnumType
 {
 
-    public function getValues()
+    public function getValues(): array
     {
         return [
             [
@@ -37,7 +37,7 @@ public function getValues()
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return 'Episode';
     }
diff --git a/tests/StarWars/Schema/HumanType.php b/tests/StarWars/Schema/HumanType.php
index 8d02d346..a0fa6417 100644
--- a/tests/StarWars/Schema/HumanType.php
+++ b/tests/StarWars/Schema/HumanType.php
@@ -8,6 +8,7 @@
 namespace Youshido\Tests\StarWars\Schema;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
 use Youshido\GraphQL\Type\ListType\ListType;
 use Youshido\GraphQL\Type\NonNullType;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
@@ -18,14 +19,14 @@
 class HumanType extends AbstractObjectType
 {
 
-    public function build($config)
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('id', new NonNullType(new IdType()))
             ->addField('name', new NonNullType(new StringType()))
             ->addField('friends', [
                 'type'    => new ListType(new CharacterInterface()),
-                'resolve' => function ($droid) {
+                'resolve' => static function ($droid) {
                     return StarWarsData::getFriends($droid);
                 },
             ])
diff --git a/tests/StarWars/Schema/StarWarsData.php b/tests/StarWars/Schema/StarWarsData.php
index d2d28607..2ced5280 100644
--- a/tests/StarWars/Schema/StarWarsData.php
+++ b/tests/StarWars/Schema/StarWarsData.php
@@ -10,7 +10,7 @@
 
 class StarWarsData
 {
-    private static function luke()
+    private static function luke(): array
     {
         return [
             'id'         => '1000',
@@ -21,7 +21,7 @@ private static function luke()
         ];
     }
 
-    private static function vader()
+    private static function vader(): array
     {
         return [
             'id'         => '1001',
@@ -32,7 +32,7 @@ private static function vader()
         ];
     }
 
-    private static function han()
+    private static function han(): array
     {
         return [
             'id'        => '1002',
@@ -42,7 +42,7 @@ private static function han()
         ];
     }
 
-    private static function leia()
+    private static function leia(): array
     {
         return [
             'id'         => '1003',
@@ -53,7 +53,7 @@ private static function leia()
         ];
     }
 
-    private static function tarkin()
+    private static function tarkin(): array
     {
         return [
             'id'        => '1004',
@@ -63,7 +63,7 @@ private static function tarkin()
         ];
     }
 
-    static function humans()
+    public static function humans(): array
     {
         return [
             '1000' => self::luke(),
@@ -74,7 +74,7 @@ static function humans()
         ];
     }
 
-    private static function threepio()
+    private static function threepio(): array
     {
         return [
             'id'              => '2000',
@@ -89,7 +89,7 @@ private static function threepio()
      * We export artoo directly because the schema returns him
      * from a root field, and hence needs to reference him.
      */
-    static function artoo()
+    public static function artoo(): array
     {
         return [
 
@@ -101,7 +101,7 @@ static function artoo()
         ];
     }
 
-    static function droids()
+    public static function droids(): array
     {
         return [
             '2000' => self::threepio(),
@@ -112,13 +112,14 @@ static function droids()
     /**
      * Helper function to get a character by ID.
      */
-    static function getCharacter($id)
+    public static function getCharacter($id)
     {
         $humans = self::humans();
         $droids = self::droids();
         if (isset($humans[$id])) {
             return $humans[$id];
         }
+        
         if (isset($droids[$id])) {
             return $droids[$id];
         }
@@ -130,7 +131,7 @@ static function getCharacter($id)
      * @param $episode
      * @return array
      */
-    static function getHero($episode)
+    public static function getHero($episode)
     {
         if ($episode === 5) {
             // Luke is the hero of Episode V.
@@ -144,7 +145,7 @@ static function getHero($episode)
     /**
      * Allows us to query for a character's friends.
      */
-    static function getFriends($character)
+    public static function getFriends(array $character): array
     {
         return array_map([__CLASS__, 'getCharacter'], $character['friends']);
     }
diff --git a/tests/StarWars/Schema/StarWarsQueryType.php b/tests/StarWars/Schema/StarWarsQueryType.php
index e54f072d..eff36246 100644
--- a/tests/StarWars/Schema/StarWarsQueryType.php
+++ b/tests/StarWars/Schema/StarWarsQueryType.php
@@ -8,8 +8,9 @@
 namespace Youshido\Tests\StarWars\Schema;
 
 
+use Youshido\GraphQL\Config\Object\ObjectTypeConfig;
+use Youshido\GraphQL\Exception\ConfigurationException;
 use Youshido\GraphQL\Field\Field;
-use Youshido\GraphQL\Field\FieldFactory;
 use Youshido\GraphQL\Type\Object\AbstractObjectType;
 use Youshido\GraphQL\Type\Scalar\IdType;
 
@@ -19,12 +20,15 @@ class StarWarsQueryType extends AbstractObjectType
     /**
      * @return String type name
      */
-    public function getName()
+    public function getName(): string
     {
         return 'Query';
     }
 
-    public function build($config)
+    /**
+     * @throws ConfigurationException
+     */
+    public function build(ObjectTypeConfig $config): void
     {
         $config
             ->addField('hero', [
@@ -32,8 +36,8 @@ public function build($config)
                 'args'    => [
                     'episode' => ['type' => new EpisodeEnum()]
                 ],
-                'resolve' => function ($root, $args) {
-                    return StarWarsData::getHero(isset($args['episode']) ? $args['episode'] : null);
+                'resolve' => static function ($root, array $args) {
+                    return StarWarsData::getHero($args['episode'] ?? null);
                 },
             ])
             ->addField(new Field([
@@ -42,10 +46,9 @@ public function build($config)
                 'args'    => [
                     'id' => new IdType()
                 ],
-                'resolve' => function ($value = null, $args = []) {
+                'resolve' => static function ($value = null, array $args = []) {
                     $humans = StarWarsData::humans();
-
-                    return isset($humans[$args['id']]) ? $humans[$args['id']] : null;
+                    return $humans[$args['id']] ?? null;
                 }
             ]))
             ->addField(new Field([
@@ -54,10 +57,9 @@ public function build($config)
                 'args'    => [
                     'id' => new IdType()
                 ],
-                'resolve' => function ($value = null, $args = []) {
+                'resolve' => static function ($value = null, array $args = []) {
                     $droids = StarWarsData::droids();
-
-                    return isset($droids[$args['id']]) ? $droids[$args['id']] : null;
+                    return $droids[$args['id']] ?? null;
                 }
             ]));
     }
diff --git a/tests/StarWars/Schema/StarWarsSchema.php b/tests/StarWars/Schema/StarWarsSchema.php
index 1ed58262..2a72ad3d 100644
--- a/tests/StarWars/Schema/StarWarsSchema.php
+++ b/tests/StarWars/Schema/StarWarsSchema.php
@@ -14,7 +14,7 @@
 class StarWarsSchema extends AbstractSchema
 {
 
-    public function build(SchemaConfig $config)
+    public function build(SchemaConfig $config): void
     {
         $config->setQuery(new StarWarsQueryType());
     }
diff --git a/tests/StarWars/StarWarsTest.php b/tests/StarWars/StarWarsTest.php
index 7f69a4b2..01874035 100644
--- a/tests/StarWars/StarWarsTest.php
+++ b/tests/StarWars/StarWarsTest.php
@@ -21,7 +21,7 @@ class StarWarsTest extends \PHPUnit_Framework_TestCase
      *
      * @dataProvider dataProvider
      */
-    public function testSchema($query, $validResult, $variables)
+    public function testSchema($query, $validResult, $variables): void
     {
         $processor = new Processor(new StarWarsSchema());
 
@@ -31,7 +31,7 @@ public function testSchema($query, $validResult, $variables)
         $this->assertEquals($validResult, $responseData);
     }
 
-    public function testInvalidVariableType()
+    public function testInvalidVariableType(): void
     {
         $processor = new Processor(new StarWarsSchema());