Notice: Undefined index: mytheme in advanced_forum_style_lineage() (row 66 of advanced_forum/includes/style.inc)

I updated to alpha3 on my Drupal 7 site the other day and now I get this error.

What do I need to attach? What could be the solution?

UPDATE: Just as I clicked save, I thought about checking the dirs - my theme where gone.
Issue resolved.

Perhaps Advanced Forum should have a fallback if set theme is missing?