diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 141b98f..ca7bc62 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1958,7 +1958,7 @@ function module_implements($hook) {
  *
  * @see \Drupal\Core\Extension\ModuleHandler::invoke()
  */
-function module_invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL) {
+function module_invoke($module, $hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL) {
   return \Drupal::moduleHandler()->invoke($module, $hook, $context1, $context2, $context3, $context4);
 }
 
@@ -1970,7 +1970,7 @@ function module_invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$c
  *
  * @see \Drupal\Core\Extension\ModuleHandler::invokeAll()
  */
-function module_invoke_all($hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL) {
+function module_invoke_all($hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL) {
   return \Drupal::moduleHandler()->invokeAll($hook, $context1, $context2, $context3, $context4);
 }
 
diff --git a/core/lib/Drupal/Core/Entity/EntityFormController.php b/core/lib/Drupal/Core/Entity/EntityFormController.php
index 3c2c92b..14484e5 100644
--- a/core/lib/Drupal/Core/Entity/EntityFormController.php
+++ b/core/lib/Drupal/Core/Entity/EntityFormController.php
@@ -411,11 +411,9 @@ protected function prepareInvokeAll($hook, array &$form_state) {
     $implementations = $this->moduleHandler->getImplementations($hook);
     foreach ($implementations as $module) {
       $function = $module . '_' . $hook;
-      if (function_exists($function)) {
-        // Ensure to pass an updated form display at each invocation, since it
-        // depends on form state which is alterable.
-        $function($this->entity, $this->getFormDisplay($form_state), $this->operation, $form_state);
-      }
+      // Ensure to pass an updated form display at each invocation, since it
+      // depends on form state which is alterable.
+      $function($this->entity, $this->getFormDisplay($form_state), $this->operation, $form_state);
     }
   }
 
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandler.php b/core/lib/Drupal/Core/Extension/ModuleHandler.php
index 51e6575..7893662 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandler.php
@@ -264,7 +264,7 @@ public function implementsHook($module, $hook) {
   /**
    * Implements \Drupal\Core\Extension\ModuleHandlerInterface::invoke().
    */
-  public function invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL) {
+  public function invoke($module, $hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL) {
     if (!$this->implementsHook($module, $hook)) {
       return;
     }
@@ -275,7 +275,7 @@ public function invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$c
   /**
    * Implements \Drupal\Core\Extension\ModuleHandlerInterface::invokeAll().
    */
-  public function invokeAll($hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL) {
+  public function invokeAll($hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL) {
     $return = array();
     $implementations = $this->getImplementations($hook);
     foreach ($implementations as $module) {
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
index c41e1d7..c58691a 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
@@ -193,7 +193,7 @@ public function implementsHook($module, $hook);
    * @return mixed
    *   The return value of the hook implementation.
    */
-  public function invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL);
+  public function invoke($module, $hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL);
 
   /**
    * Invokes a hook in all enabled modules that implement it.
@@ -215,7 +215,7 @@ public function invoke($module, $hook, &$context1 = NULL, &$context2 = NULL, &$c
    *   An array of return values of the hook implementations. If modules return
    *   arrays from their implementations, those are merged into one array.
    */
-  public function invokeAll($hook, &$context1 = NULL, &$context2 = NULL, &$context3 = NULL, &$context4 = NULL);
+  public function invokeAll($hook, $context1 = NULL, $context2 = NULL, $context3 = NULL, $context4 = NULL);
 
   /**
    * Passes alterable variables to specific hook_TYPE_alter() implementations.