Issue #2190421 by amateescu: Fix some services that shouldn't be serialized.

core/lib/Drupal/Core/Entity/ContentEntityBase.php

@@ -338,6 +338,10 @@ abstract class ContentEntityBase extends Entity implements \IteratorAggregate, C
     $this->fields = array();
     $this->fieldDefinitions = NULL;
     $this->clearTranslationCache();
+
+    // Don't serialize the url generator.
+    $this->urlGenerator = NULL;
+
     return array_keys(get_object_vars($this));
   }
 

core/lib/Drupal/Core/Entity/Entity.php

@@ -394,4 +394,14 @@ abstract class Entity implements EntityInterface {
     return $this->urlGenerator;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function __sleep() {
+    // Don't serialize the url generator.
+    $this->urlGenerator = NULL;
+
+    return array_keys(get_object_vars($this));
+  }
+
 }

core/modules/comment/lib/Drupal/comment/CommentFormController.php

@@ -30,6 +30,13 @@ class CommentFormController extends ContentEntityFormController {
    */
   protected $fieldInfo;
 
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $currentUser;
+
   /**
    * {@inheritdoc}
    */