This was a fun Kata! Thanks

I have all the tests passing, but for some reason on the last piece I am getting this message which causes an error:
Advanced Anticheat for Check luck for NaN times - Let's do it again
I am wondering why I am getting NaN here. Can you help me understand where this number comes from so that I make sure to not destroy it while solving this Kata.

I have done several roman numerals and this was the first that tested for invalid values. Very nice addition.