diff --git a/core/lib/Drupal/Core/Entity/EntityFormController.php b/core/lib/Drupal/Core/Entity/EntityFormController.php
index 675fa98..078a8f3 100644
--- a/core/lib/Drupal/Core/Entity/EntityFormController.php
+++ b/core/lib/Drupal/Core/Entity/EntityFormController.php
@@ -64,7 +64,7 @@ public function getBaseFormID() {
     // twice otherwise.
     $base_form_id = $this->entity->entityType() . '_form';
     if ($base_form_id == $this->getFormID()) {
-      $base_form_id = '';
+      $base_form_id = NULL;
     }
     return $base_form_id;
   }