Fix CollectionType form inheritance

Form/Type/CollectionType.php

@@ -36,6 +36,14 @@ class CollectionType extends AbstractType
         $builder->addEventSubscriber($listener);
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    public function getParent()
+    {
+        return 'field';
+    }
+
     /**
      * {@inheritDoc}
      */