What happens when self.select() returns size 0?

[ninehusky]

I think this is probably fine; I just want to merge a PR and don't want to dig to the bottom of this. hashtag bias for action.

Anyways: I had to put a check here which says "do nothing" if self.select().is_empty(). Is this expected behavior?

This check doesn't exist in the total ruleset synthesis because it probably doesn't matter; we don't need to unwrap that latest rule which was added and do the condition checking in that case. But because we do need to unwrap in the conditional case, this causes problems when select returns an empty set. We should see if this is ok.