State is not saved for Entity Field with 'Hidden' widget

This is how the module works at the moment. The 'Hidden' widget (added by core) does not by default call the Workflow code. Perhaps this will be corrected some time in the future.

The functions FieldItemBase::preSave() and postSave() are called, when the Hidden widget is choosen, but only if the field already exists on the entity.

The following Core issues exist:
#2159951: Allow - Hidden - as a default widget type
#2060705: Remove the 'hidden widget' plugin, it is actually never used
#2378947: Hiding a field using form modes should not remove it from the form object

I located an error in (the call to) WorkflowManager::executeTransitionsOfEntity, in below code.
We could change something there, or in the calling code. I just added the line with continue, but it causes that the entity is created without any field value.

      // Transition is created in widget or WorkflowTransitionForm.
      /* @var $transition WorkflowTransitionInterface */
      $transition = $entity->$field_name->__get('workflow_transition');
      if (!$transition) {
        // We come from creating/editing an entity via entity_form, with core widget or hidden Workflow widget.
        // @todo D8: CommentForm : or from a Edit form with hidden widget.
        if ($entity->original) {
          // Editing a Node with hidden Widget. State change not possible, so bail out.
          $entity->$field_name->value = $entity->original->$field_name->value;
          continue;
        }

        // Creating a Node with hidden Workflow Widget. Generate valid first transition.
        // @todo D8: Test Creating a non-Node Entity with hidden Workflow widget.
        $comment = '';

Hi, what about this solution? I attach a patch which now does not throw an error when saving an a new custom entity entry which has the workflow field hidden (which is normal for me as we have the workflow tab). The entity is already loaded and the field is already known so I just took advantage of it. Maybe this might fail for a Node entity though...

Added with correct file extension

Thanks, committed as-is.
In the mean time, we are working on D9. It seems that the Hidden widget does not exist anymore.