Console error and crash while removing 2 enchantments from a fishing pole to a blank book at the grinder
Console:
https://pastebin.com/WRErDij5
Server log:
https://pastebin.com/csY0WYHS
Client log:
https://pastebin.com/WU5KJAhD

I hadn't tested removing an enchantment from a book to a clean book yet, I wanted to grab unbreaking 3 from that pole to combine with another unbreaking 3 that's on a book with other enchantments

I think I know why this could be happening. I'll try to fix it.

I think I fixed it with 8ccf4c6. I've uploaded a new version to CurseForge, hopefully that works.

just saw the github update :)
I'll test it on the server ASAP

Happy to report that the crash is fixed, no errors in the console log, and also that removing enchantments from books does work successfully :)
Great job! Thank you so much!