add empty string if label doesn't exist (creation of the content)

Closes #3498006

src/EntityReferenceOverrideService.php

@@ -328,7 +328,7 @@ class EntityReferenceOverrideService {
     $modal_title = t('Override %entity_type in context of %bundle "%label"', [
       '%entity_type' => $referenced_entity->getEntityType()->getSingularLabel(),
       '%bundle' => ucfirst($referenced_entity_field->getEntity()->bundle()),
-      '%label' => $referenced_entity_field->getEntity()->label(),
+      '%label' => $referenced_entity_field->getEntity()->label() ?? "",
     ]);
 
     if (ModifyEntityForm::access(\Drupal::currentUser())->isForbidden()) {