Issue #3217262 by megachriz: Avoid usage of array_flip() in FeedType::__sleep().

src/Entity/FeedType.php

@@ -215,9 +215,10 @@ class FeedType extends ConfigEntityBundleBase implements FeedTypeInterface, Enti
     // \Drupal\Core\Entity\EntityType instance which can contain a
     // stringTranslation object that is not serializable.
     // @see https://www.drupal.org/project/drupal/issues/2893029
-    $vars = array_flip($vars);
-    unset($vars['pluginCollection']);
-    $vars = array_flip($vars);
+    $key = array_search('pluginCollection', $vars);
+    if ($key !== FALSE) {
+      unset($vars[$key]);
+    }
 
     return $vars;
   }