diff --git a/src/qtism/data/ExtendedAssessmentItemRef.php b/src/qtism/data/ExtendedAssessmentItemRef.php
index 41f89d34c..beb9416bf 100644
--- a/src/qtism/data/ExtendedAssessmentItemRef.php
+++ b/src/qtism/data/ExtendedAssessmentItemRef.php
@@ -163,7 +163,7 @@ class ExtendedAssessmentItemRef extends AssessmentItemRef implements IAssessment
      * @param IdentifierCollection $categories Optional categories.
      * @throws InvalidArgumentException if $identifier is not a valid QTI Identifier or $href is not a valid URI.
      */
-    public function __construct($identifier, $href, IdentifierCollection $categories = null)
+    public function __construct($identifier, $href, ?IdentifierCollection $categories = null)
     {
         parent::__construct($identifier, $href, $categories);
 
@@ -201,7 +201,7 @@ public function getOutcomeDeclarations(): OutcomeDeclarationCollection
      *
      * @param ResponseProcessing $responseProcessing A ResponseProcessing object or null if no response processing described.
      */
-    public function setResponseProcessing(ResponseProcessing $responseProcessing = null): void
+    public function setResponseProcessing(?ResponseProcessing $responseProcessing = null): void
     {
         $this->responseProcessing = $responseProcessing;
     }
@@ -231,7 +231,7 @@ public function hasResponseProcessing(): bool
      *
      * @param TemplateProcessing $templateProcessing
      */
-    public function setTemplateProcessing(TemplateProcessing $templateProcessing = null): void
+    public function setTemplateProcessing(?TemplateProcessing $templateProcessing = null): void
     {
         $this->templateProcessing = $templateProcessing;
     }
diff --git a/src/qtism/data/IAssessmentItem.php b/src/qtism/data/IAssessmentItem.php
index 985be7e51..50301a2a6 100644
--- a/src/qtism/data/IAssessmentItem.php
+++ b/src/qtism/data/IAssessmentItem.php
@@ -130,7 +130,7 @@ public function getResponseProcessing(): ?ResponseProcessing;
      *
      * @param ResponseProcessing $responseProcessing A ResponseProcessing object or null if no associated response processing.
      */
-    public function setResponseProcessing(ResponseProcessing $responseProcessing = null);
+    public function setResponseProcessing(?ResponseProcessing $responseProcessing = null);
 
     /**
      * Get the associated TemplateProcessing object.
@@ -144,7 +144,7 @@ public function getTemplateProcessing(): ?TemplateProcessing;
      *
      * @param TemplateProcessing $templateProcessing A TemplateProcessing object or null if no associated template processing.
      */
-    public function setTemplateProcessing(TemplateProcessing $templateProcessing = null);
+    public function setTemplateProcessing(?TemplateProcessing $templateProcessing = null);
 
     /**
      * Get the response variable identifiers related to endAttemptInteractions in the item content.
diff --git a/src/qtism/data/rules/TemplateCondition.php b/src/qtism/data/rules/TemplateCondition.php
index dcdb28711..7dfecd0f4 100644
--- a/src/qtism/data/rules/TemplateCondition.php
+++ b/src/qtism/data/rules/TemplateCondition.php
@@ -70,8 +70,11 @@ class TemplateCondition extends QtiComponent implements TemplateRule
      * @param TemplateElseIfCollection $templateElseIfs The collection of TemplateElseIf objects composing the template condition.
      * @param TemplateElse $templateElse An optional TemplateElse object composing the template condition.
      */
-    public function __construct(TemplateIf $templateIf, TemplateElseIfCollection $templateElseIfs = null, TemplateElse $templateElse = null)
-    {
+    public function __construct(
+        TemplateIf $templateIf,
+        ?TemplateElseIfCollection $templateElseIfs = null,
+        ?TemplateElse $templateElse = null
+    ) {
         $this->setTemplateIf($templateIf);
         $this->setTemplateElseIfs($templateElseIfs ?? new TemplateElseIfCollection());
         $this->setTemplateElse($templateElse);
diff --git a/src/qtism/runtime/expressions/ExpressionEngine.php b/src/qtism/runtime/expressions/ExpressionEngine.php
index b147d3ad6..23e77028a 100644
--- a/src/qtism/runtime/expressions/ExpressionEngine.php
+++ b/src/qtism/runtime/expressions/ExpressionEngine.php
@@ -84,7 +84,7 @@ class ExpressionEngine extends AbstractEngine
      * @param QtiComponent $expression The Expression object to be processed.
      * @param State $context (optional) The execution context. If no execution context is given, a virgin one will be set up.
      */
-    public function __construct(QtiComponent $expression, State $context = null)
+    public function __construct(QtiComponent $expression, ?State $context = null)
     {
         parent::__construct($expression, $context);
 
diff --git a/src/qtism/runtime/pci/json/MarshallingException.php b/src/qtism/runtime/pci/json/MarshallingException.php
index 13839ea91..43cccded9 100644
--- a/src/qtism/runtime/pci/json/MarshallingException.php
+++ b/src/qtism/runtime/pci/json/MarshallingException.php
@@ -43,7 +43,7 @@ class MarshallingException extends Exception implements QtiSdkPackageContentExce
      * @param int $code A machine-understandable (see class constants) error code.
      * @param Exception $previous An eventual previous Exception.
      */
-    public function __construct($message, $code = 0, Exception $previous = null)
+    public function __construct($message, $code = 0, ?Exception $previous = null)
     {
         parent::__construct($message, $code, $previous);
     }
diff --git a/src/qtism/runtime/pci/json/UnmarshallingException.php b/src/qtism/runtime/pci/json/UnmarshallingException.php
index aeea98c92..cf69ae4bd 100644
--- a/src/qtism/runtime/pci/json/UnmarshallingException.php
+++ b/src/qtism/runtime/pci/json/UnmarshallingException.php
@@ -46,7 +46,7 @@ class UnmarshallingException extends Exception
      * @param int $code A machine-understandable (see class constants) error code.
      * @param Exception $previous An eventual previous Exception.
      */
-    public function __construct($message, $code = 0, Exception $previous = null)
+    public function __construct($message, $code = 0, ?Exception $previous = null)
     {
         parent::__construct($message, $code, $previous);
     }
diff --git a/src/qtism/runtime/rendering/markup/AbstractMarkupRenderer.php b/src/qtism/runtime/rendering/markup/AbstractMarkupRenderer.php
index 4746513ad..6cc661906 100644
--- a/src/qtism/runtime/rendering/markup/AbstractMarkupRenderer.php
+++ b/src/qtism/runtime/rendering/markup/AbstractMarkupRenderer.php
@@ -44,7 +44,7 @@ abstract class AbstractMarkupRenderer implements Renderable
      *
      * @param AbstractMarkupRenderingEngine|null $renderingEngine
      */
-    public function __construct(AbstractMarkupRenderingEngine $renderingEngine = null)
+    public function __construct(?AbstractMarkupRenderingEngine $renderingEngine = null)
     {
         $this->setRenderingEngine($renderingEngine);
     }
@@ -52,7 +52,7 @@ public function __construct(AbstractMarkupRenderingEngine $renderingEngine = nul
     /**
      * @param AbstractMarkupRenderingEngine|null $renderingEngine
      */
-    public function setRenderingEngine(AbstractMarkupRenderingEngine $renderingEngine = null): void
+    public function setRenderingEngine(?AbstractMarkupRenderingEngine $renderingEngine = null): void
     {
         $this->renderingEngine = $renderingEngine;
     }
diff --git a/src/qtism/runtime/rendering/markup/AbstractMarkupRenderingEngine.php b/src/qtism/runtime/rendering/markup/AbstractMarkupRenderingEngine.php
index 4f9fe4c6c..6ad55b8b0 100644
--- a/src/qtism/runtime/rendering/markup/AbstractMarkupRenderingEngine.php
+++ b/src/qtism/runtime/rendering/markup/AbstractMarkupRenderingEngine.php
@@ -378,7 +378,7 @@ protected function getExploredComponent(): QtiComponent
      *
      * @param QtiComponent $component
      */
-    protected function setExploredComponent(QtiComponent $component = null): void
+    protected function setExploredComponent(?QtiComponent $component = null): void
     {
         $this->exploredComponent = $component;
     }
@@ -409,7 +409,7 @@ protected function getLastRendering()
      *
      * @param Interaction $interaction
      */
-    protected function setCurrentInteraction(Interaction $interaction = null): void
+    protected function setCurrentInteraction(?Interaction $interaction = null): void
     {
         $this->currentInteraction = $interaction;
     }
diff --git a/src/qtism/runtime/rendering/markup/xhtml/AbstractXhtmlRenderer.php b/src/qtism/runtime/rendering/markup/xhtml/AbstractXhtmlRenderer.php
index 320b62b65..1072150f0 100644
--- a/src/qtism/runtime/rendering/markup/xhtml/AbstractXhtmlRenderer.php
+++ b/src/qtism/runtime/rendering/markup/xhtml/AbstractXhtmlRenderer.php
@@ -64,7 +64,7 @@ abstract class AbstractXhtmlRenderer extends AbstractMarkupRenderer
      *
      * @param AbstractMarkupRenderingEngine $renderingEngine
      */
-    public function __construct(AbstractMarkupRenderingEngine $renderingEngine = null)
+    public function __construct(?AbstractMarkupRenderingEngine $renderingEngine = null)
     {
         parent::__construct($renderingEngine);
     }
diff --git a/src/qtism/runtime/rendering/markup/xhtml/BodyElementRenderer.php b/src/qtism/runtime/rendering/markup/xhtml/BodyElementRenderer.php
index 6e165cf18..2baf62185 100644
--- a/src/qtism/runtime/rendering/markup/xhtml/BodyElementRenderer.php
+++ b/src/qtism/runtime/rendering/markup/xhtml/BodyElementRenderer.php
@@ -43,7 +43,7 @@ class BodyElementRenderer extends AbstractXhtmlRenderer
      *
      * @param AbstractMarkupRenderingEngine $renderingEngine
      */
-    public function __construct(AbstractMarkupRenderingEngine $renderingEngine = null)
+    public function __construct(?AbstractMarkupRenderingEngine $renderingEngine = null)
     {
         parent::__construct($renderingEngine);
         $this->additionalClass('qti-bodyElement');
diff --git a/src/qtism/runtime/rendering/markup/xhtml/FeedbackBlockRenderer.php b/src/qtism/runtime/rendering/markup/xhtml/FeedbackBlockRenderer.php
index 71157edc6..a6673ce7e 100644
--- a/src/qtism/runtime/rendering/markup/xhtml/FeedbackBlockRenderer.php
+++ b/src/qtism/runtime/rendering/markup/xhtml/FeedbackBlockRenderer.php
@@ -45,7 +45,7 @@ class FeedbackBlockRenderer extends FeedbackElementRenderer
      *
      * @param AbstractMarkupRenderingEngine $renderingEngine
      */
-    public function __construct(AbstractMarkupRenderingEngine $renderingEngine = null)
+    public function __construct(?AbstractMarkupRenderingEngine $renderingEngine = null)
     {
         parent::__construct($renderingEngine);
         $this->transform('div');