Issue description:

The mod crash while going though the loading phase.
No other mods installed!

Version (make sure you are on the latest version before reporting):

Forge:14.23.4.2764
Mekanism:1.12.2-9.4.13.349

If a (crash)log is relevant for this issue, link it here: (It's almost always relevant)

https://pastebin.com/UzjRMgKt

Thanks for pointing to the Forge issue @tgstyles!
Should be fixed as of last forge version

I was able to duplicate the issue. No problems launching with Forge 14.23.4.2763.

Did you test it with forge 14.23.4.2764?

Yeah, crash report is similar to yours.

https://pastebin.com/ffPi6mTZ

MinecraftForge/MinecraftForge#5170