Crash when loading alongside Rockhounding Mod

[Derpford]

I'm having a crash on launch when loading this. The error which leads to the crash refers to a function inside the Rockhounding Mod, but the error only happens when I have ExternalTweaker in the mod list; when using just CraftTweaker, there's no crash.

Log:
https://paste.ee/p/0kxEh

[jonqrandom]

can confirm, i recently created an issue regarding this on their tracker (before i tracked down the source of the conflict and came here)