http://pastebin.com/3FZtfqkw
Crashed when trying to go on Anvil in JEI for Wooden Excavator, may crash with others

found out that the crash is caused by Anvil recipe, not JEI itself, as trying to put a Hammer/Excavator to enchant with an enchanting book crash

I've had a look and I can't see how that's caused by my mod. Testing what you said doesn't cause any issue with just my mod, so I think you might have a core mod or something changing something in the ToolMaterial class, or something from another mod is causing the issue somehow. Maybe they're setting a repair material as null when ItemStacks can't be null anymore?

But yeah, I don't think this is an issue with my mod. I don't set repair materials for my tools.

I think I found the culprit in D3Core, will ask them to take a look