diff --git a/src/Phug/Ast/Ast/Node.php b/src/Phug/Ast/Ast/Node.php
index 5dbdc8e9..7ed7aa64 100644
--- a/src/Phug/Ast/Ast/Node.php
+++ b/src/Phug/Ast/Ast/Node.php
@@ -31,7 +31,7 @@ class Node implements NodeInterface
      * @param NodeInterface $parent
      * @param array         $children
      */
-    public function __construct(NodeInterface $parent = null, array $children = null)
+    public function __construct(?NodeInterface $parent = null, ?array $children = null)
     {
         $this->parent = null;
         $this->children = [];
@@ -77,7 +77,7 @@ public function getParent()
     /**
      * {@inheritdoc}
      */
-    public function setParent(NodeInterface $parent = null)
+    public function setParent(?NodeInterface $parent = null)
     {
         if ($this->parent === $parent) {
             return $this;
diff --git a/src/Phug/Compiler/Compiler.php b/src/Phug/Compiler/Compiler.php
index 2a3f8eca..a998d086 100644
--- a/src/Phug/Compiler/Compiler.php
+++ b/src/Phug/Compiler/Compiler.php
@@ -499,7 +499,7 @@ public function getBlocks()
      *
      * @return ElementInterface
      */
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $nodeEvent = new NodeEvent($node);
         $this->trigger($nodeEvent);
@@ -537,7 +537,7 @@ public function compileNode(NodeInterface $node, ElementInterface $parent = null
      * @param BlockElement $block
      * @param array        $children
      */
-    public function replaceBlock(BlockElement $block, array $children = null)
+    public function replaceBlock(BlockElement $block, ?array $children = null)
     {
         if ($parent = $block->getParent()) {
             foreach (array_reverse($children ?: $block->getChildren()) as $child) {
diff --git a/src/Phug/Compiler/Compiler/AbstractNodeCompiler.php b/src/Phug/Compiler/Compiler/AbstractNodeCompiler.php
index 44b69d5e..17ca62a6 100644
--- a/src/Phug/Compiler/Compiler/AbstractNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/AbstractNodeCompiler.php
@@ -41,7 +41,7 @@ public function getCompiler()
      *
      * @return ElementInterface[]
      */
-    public function getCompiledNodeList($nodeList, ElementInterface $element = null)
+    public function getCompiledNodeList($nodeList, ?ElementInterface $element = null)
     {
         return array_values(array_filter(array_map(
             function (NodeInterface $childNode) use ($element) {
@@ -59,7 +59,7 @@ function (NodeInterface $childNode) use ($element) {
      *
      * @return ElementInterface[]
      */
-    public function getCompiledChildren(NodeInterface $node, ElementInterface $element = null)
+    public function getCompiledChildren(NodeInterface $node, ?ElementInterface $element = null)
     {
         return $this->getCompiledNodeList($node->getChildren(), $element);
     }
@@ -71,7 +71,7 @@ public function getCompiledChildren(NodeInterface $node, ElementInterface $eleme
      * @param NodeInterface         $node
      * @param ElementInterface|null $element
      */
-    public function compileNodeChildren(NodeInterface $node, ElementInterface $element = null)
+    public function compileNodeChildren(NodeInterface $node, ?ElementInterface $element = null)
     {
         $children = array_filter($node->getChildren());
         array_walk($children, function (NodeInterface $childNode) use ($element) {
@@ -109,7 +109,7 @@ protected function getTextChildren(ParserNodeInterface $node)
         }, $children));
     }
 
-    private function compileParserNode(NodeInterface $node, ElementInterface $element = null)
+    private function compileParserNode(NodeInterface $node, ?ElementInterface $element = null)
     {
         return $node instanceof ParserNodeInterface
             ? $this->getCompiler()->compileNode($node, $element)
diff --git a/src/Phug/Compiler/Compiler/Element/BlockElement.php b/src/Phug/Compiler/Compiler/Element/BlockElement.php
index 01760b93..5f63dc1e 100644
--- a/src/Phug/Compiler/Compiler/Element/BlockElement.php
+++ b/src/Phug/Compiler/Compiler/Element/BlockElement.php
@@ -22,9 +22,9 @@ class BlockElement extends AbstractElement
     public function __construct(
         CompilerInterface $compiler,
         $name = '',
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         $blocks = &$compiler->getBlocksByName($name);
         $blocks[] = $this;
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentListNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentListNodeCompiler.php
index 0c2796b7..422abe2c 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentListNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentListNodeCompiler.php
@@ -9,7 +9,7 @@
 
 class AssignmentListNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof AssignmentListNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentNodeCompiler.php
index 74df6392..df486878 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/AssignmentNodeCompiler.php
@@ -13,7 +13,7 @@
 
 class AssignmentNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof AssignmentNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/AttributeListNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/AttributeListNodeCompiler.php
index 3ac88694..3e900d27 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/AttributeListNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/AttributeListNodeCompiler.php
@@ -9,7 +9,7 @@
 
 class AttributeListNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof AttributeListNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/AttributeNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/AttributeNodeCompiler.php
index 896c9145..1b560efd 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/AttributeNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/AttributeNodeCompiler.php
@@ -57,7 +57,7 @@ protected function compileValue(AttributeNode $node)
         return $value;
     }
 
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof AttributeNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/BlockNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/BlockNodeCompiler.php
index b841d51f..dbf97744 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/BlockNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/BlockNodeCompiler.php
@@ -12,7 +12,7 @@
 
 class BlockNodeCompiler extends AbstractNodeCompiler
 {
-    protected function compileAnonymousBlock(BlockNode $node, ElementInterface $parent = null)
+    protected function compileAnonymousBlock(BlockNode $node, ?ElementInterface $parent = null)
     {
         $mixin = $node;
         while ($mixin->hasParent() && !($mixin instanceof MixinNode)) {
@@ -38,7 +38,7 @@ protected function hasBlockParent(BlockNode $node)
         return false;
     }
 
-    protected function compileNamedBlock($name, BlockNode $node, ElementInterface $parent = null)
+    protected function compileNamedBlock($name, BlockNode $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $layout = $compiler->getLayout();
@@ -63,7 +63,7 @@ protected function compileNamedBlock($name, BlockNode $node, ElementInterface $p
         );
     }
 
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof BlockNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/CaseNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/CaseNodeCompiler.php
index 5ea95d92..0d6f5a1b 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/CaseNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/CaseNodeCompiler.php
@@ -8,7 +8,7 @@
 
 class CaseNodeCompiler extends AbstractStatementNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof CaseNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/CodeNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/CodeNodeCompiler.php
index ad3803e4..c2ca1018 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/CodeNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/CodeNodeCompiler.php
@@ -12,7 +12,7 @@
 
 class CodeNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof CodeNode,
@@ -42,7 +42,7 @@ public function compileNode(NodeInterface $node, ElementInterface $parent = null
         return $code;
     }
 
-    private function getCodeElement(CodeNode $node, array $texts, array $children, ElementInterface $parent = null)
+    private function getCodeElement(CodeNode $node, array $texts, array $children, ?ElementInterface $parent = null)
     {
         if (count($texts) === count($children)) {
             return new CodeElement($this->getTextChildren($node), $node);
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/CommentNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/CommentNodeCompiler.php
index 8c523caf..3308b24b 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/CommentNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/CommentNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class CommentNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof CommentNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/ConditionalNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/ConditionalNodeCompiler.php
index 03b8c723..680e0df8 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/ConditionalNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/ConditionalNodeCompiler.php
@@ -9,7 +9,7 @@
 
 class ConditionalNodeCompiler extends AbstractStatementNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
 
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/DoNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/DoNodeCompiler.php
index 96a50022..0fdd3941 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/DoNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/DoNodeCompiler.php
@@ -8,7 +8,7 @@
 
 class DoNodeCompiler extends AbstractStatementNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof DoNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/DoctypeNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/DoctypeNodeCompiler.php
index 20cf4221..bfa63e19 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/DoctypeNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/DoctypeNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class DoctypeNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/DocumentNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/DocumentNodeCompiler.php
index 5ce327de..429bcc7e 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/DocumentNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/DocumentNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class DocumentNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof DocumentNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/EachNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/EachNodeCompiler.php
index 711340be..6becd93a 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/EachNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/EachNodeCompiler.php
@@ -76,7 +76,7 @@ protected function compileLoop(NodeInterface $node, $items, $key, $item)
         return $loop;
     }
 
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof EachNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/ElementNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/ElementNodeCompiler.php
index e342b0e8..ad5e6b77 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/ElementNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/ElementNodeCompiler.php
@@ -14,7 +14,7 @@
 
 class ElementNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/ExpressionNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/ExpressionNodeCompiler.php
index 5f0ccd7d..ba0f175c 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/ExpressionNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/ExpressionNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class ExpressionNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof ExpressionNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/FilterNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/FilterNodeCompiler.php
index 28168aac..daa61b08 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/FilterNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/FilterNodeCompiler.php
@@ -40,7 +40,7 @@ protected function compileText($name, $children, $parent, $indentLevel)
         }, $children));
     }
 
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/ForNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/ForNodeCompiler.php
index cd2a077c..3511369d 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/ForNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/ForNodeCompiler.php
@@ -8,7 +8,7 @@
 
 class ForNodeCompiler extends EachNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof ForNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/ImportNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/ImportNodeCompiler.php
index 70434387..7d53017a 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/ImportNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/ImportNodeCompiler.php
@@ -51,7 +51,7 @@ protected function isPugImport($path)
      *
      * @return null|ElementInterface
      */
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/KeywordNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/KeywordNodeCompiler.php
index 2abc3bf3..09daa8ee 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/KeywordNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/KeywordNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class KeywordNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof KeywordNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/MixinCallNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/MixinCallNodeCompiler.php
index e59c085a..1aa123ea 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/MixinCallNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/MixinCallNodeCompiler.php
@@ -14,7 +14,7 @@
 
 class MixinCallNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(ParserNodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(ParserNodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/MixinNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/MixinNodeCompiler.php
index 0bde5c7c..d5e15be2 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/MixinNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/MixinNodeCompiler.php
@@ -13,7 +13,7 @@
 
 class MixinNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/TextNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/TextNodeCompiler.php
index 32777615..4cc4277c 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/TextNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/TextNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class TextNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof TextNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/VariableNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/VariableNodeCompiler.php
index e8dde980..c673f884 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/VariableNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/VariableNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class VariableNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/WhenNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/WhenNodeCompiler.php
index edffac6d..1c998bf7 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/WhenNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/WhenNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class WhenNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $this->getCompiler()->assert(
             $node instanceof WhenNode,
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/WhileNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/WhileNodeCompiler.php
index 7e949cfd..95ccc02b 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/WhileNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/WhileNodeCompiler.php
@@ -9,7 +9,7 @@
 
 class WhileNodeCompiler extends AbstractStatementNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompiler/YieldNodeCompiler.php b/src/Phug/Compiler/Compiler/NodeCompiler/YieldNodeCompiler.php
index b9e102c0..97fa9f21 100644
--- a/src/Phug/Compiler/Compiler/NodeCompiler/YieldNodeCompiler.php
+++ b/src/Phug/Compiler/Compiler/NodeCompiler/YieldNodeCompiler.php
@@ -10,7 +10,7 @@
 
 class YieldNodeCompiler extends AbstractNodeCompiler
 {
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null)
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null)
     {
         $compiler = $this->getCompiler();
         $compiler->assert(
diff --git a/src/Phug/Compiler/Compiler/NodeCompilerInterface.php b/src/Phug/Compiler/Compiler/NodeCompilerInterface.php
index 1522f816..02e15b49 100644
--- a/src/Phug/Compiler/Compiler/NodeCompilerInterface.php
+++ b/src/Phug/Compiler/Compiler/NodeCompilerInterface.php
@@ -16,7 +16,7 @@ interface NodeCompilerInterface
      *
      * @return array
      */
-    public function getCompiledNodeList($nodeList, ElementInterface $parent = null);
+    public function getCompiledNodeList($nodeList, ?ElementInterface $parent = null);
 
     /**
      * @param NodeInterface    $node
@@ -24,7 +24,7 @@ public function getCompiledNodeList($nodeList, ElementInterface $parent = null);
      *
      * @return array
      */
-    public function getCompiledChildren(NodeInterface $node, ElementInterface $parent = null);
+    public function getCompiledChildren(NodeInterface $node, ?ElementInterface $parent = null);
 
     /**
      * @param NodeInterface         $node
@@ -32,7 +32,7 @@ public function getCompiledChildren(NodeInterface $node, ElementInterface $paren
      *
      * @return mixed
      */
-    public function compileNodeChildren(NodeInterface $node, ElementInterface $element = null);
+    public function compileNodeChildren(NodeInterface $node, ?ElementInterface $element = null);
 
     /**
      * @param ParserNodeInterface $node
@@ -40,7 +40,7 @@ public function compileNodeChildren(NodeInterface $node, ElementInterface $eleme
      *
      * @return null|BlockElement|ElementInterface
      */
-    public function compileNode(ParserNodeInterface $node, ElementInterface $parent = null);
+    public function compileNode(ParserNodeInterface $node, ?ElementInterface $parent = null);
 
     /**
      * @return CompilerInterface
diff --git a/src/Phug/Compiler/CompilerInterface.php b/src/Phug/Compiler/CompilerInterface.php
index ff36a9ba..3d5335b7 100644
--- a/src/Phug/Compiler/CompilerInterface.php
+++ b/src/Phug/Compiler/CompilerInterface.php
@@ -92,7 +92,7 @@ public function getBlocks();
      * @param BlockElement $block
      * @param array        $children
      */
-    public function replaceBlock(BlockElement $block, array $children = null);
+    public function replaceBlock(BlockElement $block, ?array $children = null);
 
     /**
      * @throws CompilerException
@@ -133,7 +133,7 @@ public function getCurrentImportPaths();
      *
      * @return null|ElementInterface
      */
-    public function compileNode(NodeInterface $node, ElementInterface $parent = null);
+    public function compileNode(NodeInterface $node, ?ElementInterface $parent = null);
 
     /**
      * @param string $input
diff --git a/src/Phug/Formatter/Formatter/AbstractElement.php b/src/Phug/Formatter/Formatter/AbstractElement.php
index 6250c586..a9cd649a 100644
--- a/src/Phug/Formatter/Formatter/AbstractElement.php
+++ b/src/Phug/Formatter/Formatter/AbstractElement.php
@@ -20,7 +20,7 @@ abstract class AbstractElement extends Node implements ElementInterface
      * @param NodeInterface|null $parent
      * @param array|null         $children
      */
-    public function __construct(ParserNode $originNode = null, NodeInterface $parent = null, array $children = null)
+    public function __construct(?ParserNode $originNode = null, ?NodeInterface $parent = null, ?array $children = null)
     {
         $this->originNode = $originNode;
 
diff --git a/src/Phug/Formatter/Formatter/AbstractFormat.php b/src/Phug/Formatter/Formatter/AbstractFormat.php
index d49365cf..6ce9ae0e 100644
--- a/src/Phug/Formatter/Formatter/AbstractFormat.php
+++ b/src/Phug/Formatter/Formatter/AbstractFormat.php
@@ -77,7 +77,7 @@ abstract class AbstractFormat implements FormatInterface, OptionInterface
      */
     private $debugCommentPattern = null;
 
-    public function __construct(Formatter $formatter = null)
+    public function __construct(?Formatter $formatter = null)
     {
         $patterns = [
             'class_attribute'        => static::CLASS_ATTRIBUTE,
@@ -1003,7 +1003,7 @@ protected function formatDocumentElement(DocumentElement $document)
         return $this->formatElementChildren($document, 0);
     }
 
-    protected function throwException($message, ElementInterface $element = null)
+    protected function throwException($message, ?ElementInterface $element = null)
     {
         $location = ($node = $element->getOriginNode()) && ($loc = $node->getSourceLocation())
             ? clone $loc
diff --git a/src/Phug/Formatter/Formatter/Element/AbstractValueElement.php b/src/Phug/Formatter/Formatter/Element/AbstractValueElement.php
index 3146ebd1..43d841a9 100644
--- a/src/Phug/Formatter/Formatter/Element/AbstractValueElement.php
+++ b/src/Phug/Formatter/Formatter/Element/AbstractValueElement.php
@@ -21,9 +21,9 @@ abstract class AbstractValueElement extends AbstractElement
      */
     public function __construct(
         $value = null,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/AnonymousBlockElement.php b/src/Phug/Formatter/Formatter/Element/AnonymousBlockElement.php
index 0730e70b..0dc0e775 100644
--- a/src/Phug/Formatter/Formatter/Element/AnonymousBlockElement.php
+++ b/src/Phug/Formatter/Formatter/Element/AnonymousBlockElement.php
@@ -7,7 +7,7 @@
 
 class AnonymousBlockElement extends ExpressionElement
 {
-    public function __construct(ParserNode $originNode = null, NodeInterface $parent = null, array $children = null)
+    public function __construct(?ParserNode $originNode = null, ?NodeInterface $parent = null, ?array $children = null)
     {
         parent::__construct('$__pug_children(get_defined_vars())', $originNode, $parent, $children);
         $this->uncheck();
diff --git a/src/Phug/Formatter/Formatter/Element/AssignmentElement.php b/src/Phug/Formatter/Formatter/Element/AssignmentElement.php
index 2bbcd6a9..8456169a 100644
--- a/src/Phug/Formatter/Formatter/Element/AssignmentElement.php
+++ b/src/Phug/Formatter/Formatter/Element/AssignmentElement.php
@@ -31,11 +31,11 @@ class AssignmentElement extends AbstractElement implements AttributesInterface,
      */
     public function __construct(
         $name,
-        SplObjectStorage $attributes = null,
-        AssignmentContainerInterface $container = null,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?SplObjectStorage $attributes = null,
+        ?AssignmentContainerInterface $container = null,
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/AttributeElement.php b/src/Phug/Formatter/Formatter/Element/AttributeElement.php
index 9e929b17..b4baeead 100644
--- a/src/Phug/Formatter/Formatter/Element/AttributeElement.php
+++ b/src/Phug/Formatter/Formatter/Element/AttributeElement.php
@@ -27,9 +27,9 @@ class AttributeElement extends AbstractValueElement implements OrderableInterfac
     public function __construct(
         $name,
         $value,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/CodeElement.php b/src/Phug/Formatter/Formatter/Element/CodeElement.php
index d240a77c..dfac2013 100644
--- a/src/Phug/Formatter/Formatter/Element/CodeElement.php
+++ b/src/Phug/Formatter/Formatter/Element/CodeElement.php
@@ -34,9 +34,9 @@ class CodeElement extends AbstractValueElement implements TransformableInterface
      */
     public function __construct(
         $value = null,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($value, $originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/KeywordElement.php b/src/Phug/Formatter/Formatter/Element/KeywordElement.php
index 7b3ad80b..518f2166 100644
--- a/src/Phug/Formatter/Formatter/Element/KeywordElement.php
+++ b/src/Phug/Formatter/Formatter/Element/KeywordElement.php
@@ -27,9 +27,9 @@ class KeywordElement extends AbstractElement
     public function __construct(
         $name,
         $value,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/MarkupElement.php b/src/Phug/Formatter/Formatter/Element/MarkupElement.php
index a79cc2d4..694a3fec 100644
--- a/src/Phug/Formatter/Formatter/Element/MarkupElement.php
+++ b/src/Phug/Formatter/Formatter/Element/MarkupElement.php
@@ -32,10 +32,10 @@ class MarkupElement extends AbstractMarkupElement implements AttributesInterface
     public function __construct(
         $name,
         $autoClosed = false,
-        SplObjectStorage $attributes = null,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?SplObjectStorage $attributes = null,
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Element/VariableElement.php b/src/Phug/Formatter/Formatter/Element/VariableElement.php
index 0438cb8a..26df0229 100644
--- a/src/Phug/Formatter/Formatter/Element/VariableElement.php
+++ b/src/Phug/Formatter/Formatter/Element/VariableElement.php
@@ -28,11 +28,11 @@ class VariableElement extends AbstractElement
      * @param array|null             $children
      */
     public function __construct(
-        CodeElement $variable = null,
-        ExpressionElement $expression = null,
-        ParserNode $originNode = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?CodeElement $variable = null,
+        ?ExpressionElement $expression = null,
+        ?ParserNode $originNode = null,
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($originNode, $parent, $children);
 
diff --git a/src/Phug/Formatter/Formatter/Event/FormatEvent.php b/src/Phug/Formatter/Formatter/Event/FormatEvent.php
index 30b0a8fc..07469a71 100644
--- a/src/Phug/Formatter/Formatter/Event/FormatEvent.php
+++ b/src/Phug/Formatter/Formatter/Event/FormatEvent.php
@@ -37,7 +37,7 @@ public function getElement()
     /**
      * @param ElementInterface $element
      */
-    public function setElement(ElementInterface $element = null)
+    public function setElement(?ElementInterface $element = null)
     {
         $this->element = $element;
     }
diff --git a/src/Phug/Formatter/Formatter/Format/HtmlFormat.php b/src/Phug/Formatter/Formatter/Format/HtmlFormat.php
index a8588627..37d471df 100644
--- a/src/Phug/Formatter/Formatter/Format/HtmlFormat.php
+++ b/src/Phug/Formatter/Formatter/Format/HtmlFormat.php
@@ -11,7 +11,7 @@ class HtmlFormat extends XhtmlFormat
     const EXPLICIT_CLOSING_TAG = '<%s/>';
     const BOOLEAN_ATTRIBUTE_PATTERN = ' %s';
 
-    public function __construct(Formatter $formatter = null)
+    public function __construct(?Formatter $formatter = null)
     {
         parent::__construct($formatter);
 
diff --git a/src/Phug/Formatter/Formatter/Format/XhtmlFormat.php b/src/Phug/Formatter/Formatter/Format/XhtmlFormat.php
index d51e5150..d5d854f2 100644
--- a/src/Phug/Formatter/Formatter/Format/XhtmlFormat.php
+++ b/src/Phug/Formatter/Formatter/Format/XhtmlFormat.php
@@ -13,7 +13,7 @@ abstract class XhtmlFormat extends XmlFormat
     const DOCTYPE_LANGUAGE = 'html';
     const SELF_CLOSING_TAG = '<%s />';
 
-    public function __construct(Formatter $formatter = null)
+    public function __construct(?Formatter $formatter = null)
     {
         $this->setOptionsRecursive([
             'white_space_sensitive_tags' => [
diff --git a/src/Phug/Formatter/Formatter/Format/XmlFormat.php b/src/Phug/Formatter/Formatter/Format/XmlFormat.php
index 757ade84..4a0c4e65 100644
--- a/src/Phug/Formatter/Formatter/Format/XmlFormat.php
+++ b/src/Phug/Formatter/Formatter/Format/XmlFormat.php
@@ -37,7 +37,7 @@ class XmlFormat extends AbstractFormat
     const BOOLEAN_ATTRIBUTE_PATTERN = ' %s="%s"';
     const BUFFER_VARIABLE = '$__value';
 
-    public function __construct(Formatter $formatter = null)
+    public function __construct(?Formatter $formatter = null)
     {
         parent::__construct($formatter);
 
diff --git a/src/Phug/Formatter/Formatter/FormatInterface.php b/src/Phug/Formatter/Formatter/FormatInterface.php
index bc0160f6..24c56615 100644
--- a/src/Phug/Formatter/Formatter/FormatInterface.php
+++ b/src/Phug/Formatter/Formatter/FormatInterface.php
@@ -11,7 +11,7 @@ interface FormatInterface
 {
     const DEFAULT_VARIABLES_VARIABLE_NAME = 'pug_vars';
 
-    public function __construct(Formatter $formatter = null);
+    public function __construct(?Formatter $formatter = null);
 
     public function format($element);
 
diff --git a/src/Phug/Formatter/Formatter/Partial/PatternTrait.php b/src/Phug/Formatter/Formatter/Partial/PatternTrait.php
index 0ee4d2cd..2cbffad4 100644
--- a/src/Phug/Formatter/Formatter/Partial/PatternTrait.php
+++ b/src/Phug/Formatter/Formatter/Partial/PatternTrait.php
@@ -98,7 +98,7 @@ public function setPatterns($patterns)
      *
      * @return string
      */
-    public function exportHelper($name, array $arguments = null)
+    public function exportHelper($name, ?array $arguments = null)
     {
         $this->requireHelper($name);
 
diff --git a/src/Phug/Lexer/Lexer/AbstractToken.php b/src/Phug/Lexer/Lexer/AbstractToken.php
index 5ff5390e..55f68b55 100644
--- a/src/Phug/Lexer/Lexer/AbstractToken.php
+++ b/src/Phug/Lexer/Lexer/AbstractToken.php
@@ -13,7 +13,7 @@ abstract class AbstractToken implements TokenInterface, HandleTokenInterface
     private $indentation;
     private $handled = false;
 
-    public function __construct(SourceLocationInterface $sourceLocation = null, $level = null, $indentation = null)
+    public function __construct(?SourceLocationInterface $sourceLocation = null, $level = null, $indentation = null)
     {
         $this->sourceLocation = $sourceLocation;
         $this->level = $level ?: 0;
diff --git a/src/Phug/Lexer/Lexer/Scanner/AttributeScanner.php b/src/Phug/Lexer/Lexer/Scanner/AttributeScanner.php
index ff6816c6..290f47e2 100644
--- a/src/Phug/Lexer/Lexer/Scanner/AttributeScanner.php
+++ b/src/Phug/Lexer/Lexer/Scanner/AttributeScanner.php
@@ -103,7 +103,7 @@ private function isExpressionPartial(Reader $reader, $expression)
         $this->isTruncatedValue($expression);
     }
 
-    private function getAttributeValue(Reader $reader, array $chars = null)
+    private function getAttributeValue(Reader $reader, ?array $chars = null)
     {
         $chars = $chars ?: [
             ' ', "\t", "\n", ',', ')', '//',
diff --git a/src/Phug/Lexer/Lexer/Scanner/IndentationScanner.php b/src/Phug/Lexer/Lexer/Scanner/IndentationScanner.php
index 00ca2b48..a4cbb0f1 100644
--- a/src/Phug/Lexer/Lexer/Scanner/IndentationScanner.php
+++ b/src/Phug/Lexer/Lexer/Scanner/IndentationScanner.php
@@ -53,7 +53,7 @@ protected function formatIndentChar(State $state, $indentChar)
         return $indentChar;
     }
 
-    public function getIndentLevel(State $state, $maxLevel = INF, callable $getIndentChar = null)
+    public function getIndentLevel(State $state, $maxLevel = INF, ?callable $getIndentChar = null)
     {
         if ($maxLevel <= 0) {
             return 0;
diff --git a/src/Phug/Lexer/Lexer/TokenInterface.php b/src/Phug/Lexer/Lexer/TokenInterface.php
index 0ed57bbc..88ed4f88 100644
--- a/src/Phug/Lexer/Lexer/TokenInterface.php
+++ b/src/Phug/Lexer/Lexer/TokenInterface.php
@@ -6,7 +6,7 @@
 
 interface TokenInterface
 {
-    public function __construct(SourceLocationInterface $sourceLocation = null, $level = null, $indentation = null);
+    public function __construct(?SourceLocationInterface $sourceLocation = null, $level = null, $indentation = null);
 
     /**
      * @return SourceLocationInterface|null
diff --git a/src/Phug/Parser/Parser/Node.php b/src/Phug/Parser/Parser/Node.php
index e23c375a..42053e83 100644
--- a/src/Phug/Parser/Parser/Node.php
+++ b/src/Phug/Parser/Parser/Node.php
@@ -34,11 +34,11 @@ class Node extends AstNode implements NodeInterface
      * @param TokenInterface               $token          the token that created the node
      */
     public function __construct(
-        TokenInterface $token = null,
-        SourceLocationInterface $sourceLocation = null,
+        ?TokenInterface $token = null,
+        ?SourceLocationInterface $sourceLocation = null,
         $level = null,
-        NodeInterface $parent = null,
-        array $children = null
+        ?NodeInterface $parent = null,
+        ?array $children = null
     ) {
         parent::__construct($parent, $children);
 
@@ -77,7 +77,7 @@ public function getToken()
      *
      * @return $this
      */
-    public function setOuterNode(NodeInterface $node = null)
+    public function setOuterNode(?NodeInterface $node = null)
     {
         $this->outerNode = $node;
 
diff --git a/src/Phug/Parser/Parser/State.php b/src/Phug/Parser/Parser/State.php
index fd0cc676..562ca30e 100644
--- a/src/Phug/Parser/Parser/State.php
+++ b/src/Phug/Parser/Parser/State.php
@@ -101,7 +101,7 @@ class State implements OptionInterface, EventManagerInterface
      */
     private $interpolationNodes;
 
-    public function __construct(Parser $parser, \Iterator $tokens, array $options = null)
+    public function __construct(Parser $parser, \Iterator $tokens, ?array $options = null)
     {
         $this->parser = $parser;
         $this->level = 0;
@@ -329,7 +329,7 @@ private function getNamedHandler($handler)
      *
      * @return $this
      */
-    public function handleToken(TokenInterface $token = null)
+    public function handleToken(?TokenInterface $token = null)
     {
         $token = $token ?: $this->getToken();
         $className = get_class($token);
@@ -534,7 +534,7 @@ public function parentNodeIs(array $classNames)
      *
      * @return Node The newly created node
      */
-    public function createNode($className, TokenInterface $token = null)
+    public function createNode($className, ?TokenInterface $token = null)
     {
         if (!is_subclass_of($className, Node::class)) {
             throw new \InvalidArgumentException(
@@ -630,7 +630,7 @@ public function store()
      *
      * @throws ParserException
      */
-    public function throwException($message, $code = 0, TokenInterface $relatedToken = null, $previous = null)
+    public function throwException($message, $code = 0, ?TokenInterface $relatedToken = null, $previous = null)
     {
         $lexer = $this->parser->getLexer();
         //This will basically check for a source location for this Node. The process is like:
diff --git a/src/Phug/Parser/ParserException.php b/src/Phug/Parser/ParserException.php
index a7bc809a..9ac517d4 100644
--- a/src/Phug/Parser/ParserException.php
+++ b/src/Phug/Parser/ParserException.php
@@ -17,7 +17,7 @@ public function __construct(
         SourceLocation $location,
         $message = '',
         $code = 0,
-        TokenInterface $relatedToken = null,
+        ?TokenInterface $relatedToken = null,
         $previous = null
     ) {
         parent::__construct($location, $message, $code, $previous);
diff --git a/src/Phug/Phug/Phug/Partial/PluginEnablerTrait.php b/src/Phug/Phug/Phug/Partial/PluginEnablerTrait.php
index 3974c421..c611d373 100644
--- a/src/Phug/Phug/Phug/Partial/PluginEnablerTrait.php
+++ b/src/Phug/Phug/Phug/Partial/PluginEnablerTrait.php
@@ -15,7 +15,7 @@ trait PluginEnablerTrait
      *
      * @throws PhugException
      */
-    public static function enable(Renderer $renderer = null)
+    public static function enable(?Renderer $renderer = null)
     {
         if ($renderer) {
             static::activateOnRenderer($renderer);
diff --git a/src/Phug/Reader/Reader.php b/src/Phug/Reader/Reader.php
index 8b28ba24..844179d3 100644
--- a/src/Phug/Reader/Reader.php
+++ b/src/Phug/Reader/Reader.php
@@ -618,7 +618,7 @@ public function peekAlphaNumeric()
      *
      * @return bool whether it could be or not.
      */
-    public function peekAlphaIdentifier(array $allowedChars = null)
+    public function peekAlphaIdentifier(?array $allowedChars = null)
     {
         $allowedChars = $allowedChars ?: ['_'];
 
@@ -632,7 +632,7 @@ public function peekAlphaIdentifier(array $allowedChars = null)
      *
      * @return bool whether it could be or not.
      */
-    public function peekIdentifier(array $allowedChars = null)
+    public function peekIdentifier(?array $allowedChars = null)
     {
         return $this->peekAlphaIdentifier($allowedChars) || $this->peekDigit();
     }
@@ -757,7 +757,7 @@ public function readIdentifier($prefix = null, $allowedChars = null)
      *
      * @return string|null the resulting string or null if none encountered.
      */
-    public function readString(array $escapeSequences = null, $raw = false)
+    public function readString(?array $escapeSequences = null, $raw = false)
     {
         if (!$this->peekQuote()) {
             return;
@@ -820,7 +820,7 @@ public function readString(array $escapeSequences = null, $raw = false)
      *
      * @return string|null the resulting expression or null, if none encountered.
      */
-    public function readExpression(array $breaks = null, array $brackets = null)
+    public function readExpression(?array $breaks = null, ?array $brackets = null)
     {
         if (!$this->hasLength()) {
             return;
diff --git a/src/Phug/Renderer/Renderer/Task/TasksGroup.php b/src/Phug/Renderer/Renderer/Task/TasksGroup.php
index e1f413a1..1a168578 100644
--- a/src/Phug/Renderer/Renderer/Task/TasksGroup.php
+++ b/src/Phug/Renderer/Renderer/Task/TasksGroup.php
@@ -11,7 +11,7 @@ class TasksGroup
     protected $success = 0;
     protected $errorDetails = [];
 
-    public function __construct(Renderer $renderer = null)
+    public function __construct(?Renderer $renderer = null)
     {
         if ($renderer) {
             $this->renderer = $renderer;
diff --git a/src/Phug/Util/Util/SandBox.php b/src/Phug/Util/Util/SandBox.php
index 2ae952af..5ab5e694 100644
--- a/src/Phug/Util/Util/SandBox.php
+++ b/src/Phug/Util/Util/SandBox.php
@@ -23,7 +23,7 @@ class SandBox
      */
     private $throwable;
 
-    public function __construct(callable $action, callable $errorInterceptor = null)
+    public function __construct(callable $action, ?callable $errorInterceptor = null)
     {
         set_error_handler($errorInterceptor ?: function ($number, $message, $file, $line) {
             if (error_reporting() & $number) {