Using my custom modpack, after trying to create a party the book won't create a party and trying to view the party list, the game just straight up crashes to desktop. I have got one party to be created successfully, however, the server will not allow any more to be created. and just crashes anyone looking at party list.

Here's the crash report.
https://gist.github.com/SirOMGitsYOU/de7ca2c96d06d260337b8b29f51cd334