Malformed HTML due to undefined variable in preview

Under circumstances where admin pages preview AT markup, the {{ html_element }} variable in some AT core templates may not be defined and result in malformed HTML.

I assume this is because html_element is normally defined in AT_core (\includes\preprocess.inc and/or \includes\misc.inc), and those functions do not run within an administration context.

This would rarely affect a site visitor, but it would be ideal if all AT twig templates using this variable had a default value to prevent this malformed HTML from displaying, regardless of whether the user is on an admin page or not.

Something like:

<{{ html_element|default('div') }}{{ attributes }}>
  {{ content }}
</{{ html_element|default('div') }}>

That said, any solution that prevented malformed HTML from showing up would be great.