Unexpected exception encountered. Not normalised type = CHAR

Hello.
I'm in the process of making a scanner for my Compiler Design class using JFlex and Cup and ran into this error. Not 100% sure if it's from my own code or something else and figured I'd report the bug anyway. Attached is the output after attempting to compile as well as a link to a repo of my current project that should reproduce the bug.

Any help at all would be appreciated thank you.