An additional check is needed in the is_interested_in_play_action method for when the number of tracks == 0. This should cause a return before the method gets the tab group (which won't be defined unless there are actual tracks, see the init method).
An additional check is needed in the is_interested_ in_play_ action method for when the number of tracks == 0. This should cause a return before the method gets the tab group (which won't be defined unless there are actual tracks, see the init method).