• Fail: checkio(undefined) means what?

Question related to mission Open Labyrinth

Last two tests (in extra section) failed, with output I believe is recursion calls or something like that. Third that failed have nicely written: RuntimeError: maximum recursion depth exceeded in cmp, and there is checkio(some board)

So, OK, I have bug to catch, but at least I have input data so I can test.

But I'm not sure what those last two even send to checkio function as data? What does that 'undefined' mean?