Error if no entity types are selected

I have resolved the issue & added patch, please review.

Thanks, that sounds reasonable.

Just two points to finish this issue:

1. Please create a merge request using forks.
2. Let's combine if checks within one statement:

Before:

 if(!empty($form[$entity_type_id])){
                 if (empty(Element::children($form[$entity_type_id]))) {
                     unset($form[$entity_type_id]);
             }

After:

 if(!empty($form[$entity_type_id]) && empty(Element::children($form[$entity_type_id]))) {
                   unset($form[$entity_type_id]);
             }

@quadrexdev, I have update the above solution & generated the MR, please review.

Merged, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.