That's great, Michael!
For now, I'll just have to not create a widget in the sidebar until I know there are posts in it. So I add it, and if I just get a title, then I remove it.
I'm really looking forward to having it not even spit out a title in the sidebar unless the taxonomy is actually populated with posts. I'm thinking that could all happen in one step, sort of? So you would still be able to create the widget in the sidebar, but if a taxonomy had no posts, it wouldn't create output or a listener. And then later, when posts got added to that one, it would print the title and the list, and create the listener.
I appreciate all you're doing!