Forge v14.23.4.2789-1.12.2
Improved Mobs v1.2.2
Paleolithic Revolution v1.1
I got this crash while creating a new world with the mod Paleolithic Revolution installed. Here's the crash log.

This appears to be a problem with Improved Mobs trying to "improve" the humans in Revolution, I would bring this up with them. Based on the source code in IM, there might be a config option to black list the Revolution mobs from being affected by this.

EDIT: I just realized this is referenced. Sorry about that.

Ok, thanks!

i dont know why the entity returns null with their registered name since normally it shouldn't. i added an nullcheck to it so it wont crash in the next update though.