Fixes T9476. Currently, if you enter no text in "arc:prompt", we abort resolution immediately.
However, this is a bit inconsistent (other rules that fail to resolve are skipped) it is reasonable to put some default rule behind "arc:prompt" so that you can just mash enter to select it. This construction is unusual, but seems fine and sensible to me.
If you're using "arc:prompt" as the last rule, the behavior is the same as before, so this should only make the rule more useful.