diff --git a/src/BehaviorInvoker.php b/src/BehaviorInvoker.php
index afbd5cc..f89297a 100644
--- a/src/BehaviorInvoker.php
+++ b/src/BehaviorInvoker.php
@@ -74,7 +74,7 @@ class BehaviorInvoker implements BehaviorInvokerInterface {
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
    */
-  public function __construct(BehaviorSettingsManager $rabbit_hole_behavior_settings_manager, RabbitHoleBehaviorPluginManager $plugin_manager_rabbit_hole_behavior_plugin, RabbitHoleEntityPluginManager $plugin_manager_rabbit_hole_entity_plugin, EntityExtender $entity_extender, AccountProxyInterface $current_user, ModuleHandlerInterface $module_handler = NULL) {
+  public function __construct(BehaviorSettingsManager $rabbit_hole_behavior_settings_manager, RabbitHoleBehaviorPluginManager $plugin_manager_rabbit_hole_behavior_plugin, RabbitHoleEntityPluginManager $plugin_manager_rabbit_hole_entity_plugin, EntityExtender $entity_extender, AccountProxyInterface $current_user, ?ModuleHandlerInterface $module_handler = NULL) {
     $this->rhBehaviorSettingsManager = $rabbit_hole_behavior_settings_manager;
     $this->rhBehaviorPluginManager = $plugin_manager_rabbit_hole_behavior_plugin;
     $this->rhEntityPluginManager = $plugin_manager_rabbit_hole_entity_plugin;
@@ -122,7 +122,7 @@ class BehaviorInvoker implements BehaviorInvokerInterface {
   /**
    * {@inheritdoc}
    */
-  public function processEntity(ContentEntityInterface $entity, Response $current_response = NULL) {
+  public function processEntity(ContentEntityInterface $entity, ?Response $current_response = NULL) {
     $plugin = $this->getBehaviorPlugin($entity);
 
     if ($plugin === NULL) {
diff --git a/src/BehaviorInvokerInterface.php b/src/BehaviorInvokerInterface.php
index e6c7ebc..a344398 100644
--- a/src/BehaviorInvokerInterface.php
+++ b/src/BehaviorInvokerInterface.php
@@ -52,7 +52,7 @@ interface BehaviorInvokerInterface {
    * @throws \Drupal\Component\Plugin\Exception\PluginException
    * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
    */
-  public function processEntity(ContentEntityInterface $entity, Response $current_response = NULL);
+  public function processEntity(ContentEntityInterface $entity, ?Response $current_response = NULL);
 
   /**
    * Load a list of entity IDs supported by rabbit hole given available plugins.
diff --git a/src/FormManglerService.php b/src/FormManglerService.php
index 7e97596..7a847b0 100644
--- a/src/FormManglerService.php
+++ b/src/FormManglerService.php
@@ -480,9 +480,9 @@ class FormManglerService {
     array &$form,
     FormStateInterface $form_state,
     $form_id,
-    EntityInterface $entity = NULL,
+    ?EntityInterface $entity = NULL,
     $entity_is_bundle = FALSE,
-    ImmutableConfig $bundle_settings = NULL
+    ?ImmutableConfig $bundle_settings = NULL
   ) {
 
     foreach ($this->rhBehaviorPluginManager->getDefinitions() as $id => $def) {
diff --git a/src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php b/src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php
index c21789b..fa47b78 100644
--- a/src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php
+++ b/src/Plugin/RabbitHoleBehaviorPlugin/AccessDenied.php
@@ -20,7 +20,7 @@ class AccessDenied extends RabbitHoleBehaviorPluginBase {
   /**
    * {@inheritdoc}
    */
-  public function performAction(EntityInterface $entity, Response $current_response = NULL) {
+  public function performAction(EntityInterface $entity, ?Response $current_response = NULL) {
     throw new AccessDeniedHttpException();
   }
 
diff --git a/src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php b/src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php
index 451b2d3..67e06e7 100644
--- a/src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php
+++ b/src/Plugin/RabbitHoleBehaviorPlugin/PageNotFound.php
@@ -20,7 +20,7 @@ class PageNotFound extends RabbitHoleBehaviorPluginBase {
   /**
    * {@inheritdoc}
    */
-  public function performAction(EntityInterface $entity, Response $current_response = NULL) {
+  public function performAction(EntityInterface $entity, ?Response $current_response = NULL) {
     throw new NotFoundHttpException();
   }
 
diff --git a/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php b/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php
index 40e1ad6..00ff3b3 100644
--- a/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php
+++ b/src/Plugin/RabbitHoleBehaviorPlugin/PageRedirect.php
@@ -114,7 +114,7 @@ class PageRedirect extends RabbitHoleBehaviorPluginBase implements ContainerFact
   /**
    * {@inheritdoc}
    */
-  public function performAction(EntityInterface $entity, Response $current_response = NULL) {
+  public function performAction(EntityInterface $entity, ?Response $current_response = NULL) {
     $target = $this->getActionTarget($entity);
     $response_code = $this->getActionResponseCode($entity);
 
@@ -254,9 +254,9 @@ class PageRedirect extends RabbitHoleBehaviorPluginBase implements ContainerFact
     array &$form,
     FormStateInterface $form_state,
     $form_id,
-    EntityInterface $entity = NULL,
+    ?EntityInterface $entity = NULL,
     $entity_is_bundle = FALSE,
-    ImmutableConfig $bundle_settings = NULL
+    ?ImmutableConfig $bundle_settings = NULL
   ) {
 
     $redirect = NULL;
diff --git a/src/Plugin/RabbitHoleBehaviorPluginBase.php b/src/Plugin/RabbitHoleBehaviorPluginBase.php
index 50c9e42..59bd90e 100644
--- a/src/Plugin/RabbitHoleBehaviorPluginBase.php
+++ b/src/Plugin/RabbitHoleBehaviorPluginBase.php
@@ -25,7 +25,7 @@ abstract class RabbitHoleBehaviorPluginBase extends PluginBase implements Rabbit
   /**
    * {@inheritdoc}
    */
-  public function settingsForm(array &$form, FormStateInterface $form_state, $form_id, EntityInterface $entity = NULL, $entity_is_bundle = FALSE, ImmutableConfig $bundle_settings = NULL) {
+  public function settingsForm(array &$form, FormStateInterface $form_state, $form_id, ?EntityInterface $entity = NULL, $entity_is_bundle = FALSE, ?ImmutableConfig $bundle_settings = NULL) {
     // Present no settings form.
   }
 
diff --git a/src/Plugin/RabbitHoleBehaviorPluginInterface.php b/src/Plugin/RabbitHoleBehaviorPluginInterface.php
index e3a8e1f..757bada 100644
--- a/src/Plugin/RabbitHoleBehaviorPluginInterface.php
+++ b/src/Plugin/RabbitHoleBehaviorPluginInterface.php
@@ -41,7 +41,7 @@ interface RabbitHoleBehaviorPluginInterface extends PluginInspectionInterface {
    *   The behavior settings for the bundle of the entity (or the entity itself,
    *   if it is a bundle).
    */
-  public function settingsForm(array &$form, FormStateInterface $form_state, $form_id, EntityInterface $entity = NULL, $entity_is_bundle = FALSE, ImmutableConfig $bundle_settings = NULL);
+  public function settingsForm(array &$form, FormStateInterface $form_state, $form_id, ?EntityInterface $entity = NULL, $entity_is_bundle = FALSE, ?ImmutableConfig $bundle_settings = NULL);
 
   /**
    * Handle submission of the settings form for this plugin.