fix: deprecations issues

Author: csemazharul

src/Exception/InvalidArgumentException.php

@@ -8,7 +8,7 @@ class InvalidArgumentException extends \Exception
 
 {
 
-    public function __construct($ruleName, $parameterCount, $code = 0, Exception $previous = null)
+    public function __construct($ruleName, $parameterCount, $code = 0, ?Exception $previous = null)
     {
         parent::__construct(sprintf("Validation rule %s requires at least %d parameters", $ruleName, $parameterCount), $code, $previous);
     }

src/Exception/MethodNotFoundException.php

@@ -7,7 +7,7 @@
 class MethodNotFoundException extends \Exception
 
 {
-    public function __construct($sanitizationMethod, $code = 0, Exception $previous = null)
+    public function __construct($sanitizationMethod, $code = 0, ?Exception $previous = null)
     {
         parent::__construct(sprintf("Unsupported sanitization method: %s.", $sanitizationMethod), $code, $previous);
     }

src/Exception/RuleErrorException.php

@@ -7,7 +7,7 @@
 class RuleErrorException extends \Exception
 
 {
-    public function __construct($ruleName, $code = 0, Exception $previous = null)
+    public function __construct($ruleName, $code = 0, ?Exception $previous = null)
     {
         parent::__construct(sprintf("Unsupported validation rule: %s.", $ruleName), $code, $previous);
     }

src/InputDataContainer.php

@@ -28,7 +28,7 @@ public function getAttributeKey()
 
     public function getAttributeValue($key = null)
     {
-        $keys = explode('.', trim($this->attributeKey, '[]'));
+        $keys = explode('.', trim($this->attributeKey ?? '', '[]'));
 
         $data = $this->data;
 
@@ -63,7 +63,7 @@ public function getData()
 
     public function setAttributeValue($value): void
     {
-        $keys = explode('.', trim($this->attributeKey, '[]'));
+        $keys = explode('.', trim($this->attributeKey ?? '', '[]'));
 
         if (\count($keys) > 1) {
             $this->setNestedElement($this->data, $keys, $value);