https://gist.github.com/Febilian/99bb7b4b63bb5f9903cd684f77a2f348

Took me a bit to connect the dots between "this update added support for hellbark trees" and "I specifically have BOP's nether biomes disabled by setting their biome IDs to -1 in the BOP config files" as a potential cause for this.

It's possible that setting any BOP biome ID to -1 will cause this crash if a tree that only generates in that specific kind of biome tries to figure out where to generate. May be worth looking into!

The problem was in Dynamic Trees base mod and I've just made a fix for it. You'll see the fix in the next alpha release whenever that is.

Thank you for your insight. It's details like this that allow us to fix problems like this rapidly.

Wow, that was certainly a fast response! Best of luck getting it working, I really love dynamic trees and the fact that it's been getting a lot of mod support lately makes it more fun to use.