What happened?
Server crashes when a player leaves.

What should happen?
Server should not crash when a player leaves.

Steps to reproduce
Install mod, join server, leave server, observe crash.

Version
Minecraft: 1.15.1
Mod version 1.1.11
Forge version: 30.0.36

Crash report if available (use https://paste.dimdev.org)
https://gist.github.com/Fenrirthviti/d477ff1c338cae788663f967d01cb405

Additional info

Fixed in new version (should be up soon on CurseForge)

Thanks!