Crashlog:
http://puu.sh/o3aes/08857fbb3f.txt

When did this occur?:
Randomly running around punching things in the world :P

Looks like the crash was caused by an inventory. Do you know what kind it was?

Nope, this happened when i simply turned around and looked at things in the world. I could jump in-game and see what i can find could have caused it.

I'll just add in a safety check. It looks like the fault of another mod, but that should at least prevent WIT from crashing. No guarantees about what will happen when the actual inventory is opened however...

Apparently it was a Grave from the Graves mod by Fireball1725
http://minecraft.curseforge.com/projects/graves?gameCategorySlug=mc-mods&projectID=240877