To reproduce, that drag Luhn CheckSum and set radix to 4 and then input to o or whatever invalid input
as you can see an unhandled thrown look like that

Luhn Checksum - Error in blob:https://gchq.github.io/8a7d4b37-1964-4435-9bed-004d1c2a45ae on line 2.<br><br>Message: Character: o is not valid in radix 4.

Direct Test Links:

• https://gchq.github.io/CyberChef/#recipe=Luhn_Checksum(4)&input=bw&oeol=FF