Issue description:

Game crashes on startup if sneak is bound to mouse button 4.
(key_key.sneak:key.mouse.4 in the options.txt file)

Steps to reproduce:

1. Bind sneak to mouse button 4
2. Restart game

Version:

Forge: forge-1.15.2-31.1.18
Mekanism: 1.15.2-9.9.11.403

Crashlog:

https://paste.ee/p/iVDqX

I don't think this issue is related to Mekanism. It appears this crash occurs without Mekanism installed as well: https://www.reddit.com/r/Minecraft/comments/eab7b9/version_115_consistently_crashes_upon_startup/

Try out the solutions mentioned in that thread and see if it helps.

That linked crash is something different. I don't get a crash without Mekanism.

The crash happens if sneak is bound to any mouse key, not just mouse 4 as I originally thought. I believe it is caused by only handling keyboard keys here. (The code for handling mouse buttons is commented out two lines above that)

Please reopen.