Encountered against Psi-r1.1-45, AutoRegLib-1.1-4, forge-1.11.2-13.20.0.2226 (with mercurius, apparently), recent Java 8.

I attempted to use the following loopcast spell (gotten from another bug) to create a wall. The spell compiles successfully, and, with a stack of e.g. cobble in the hotbar after the CAD, works until it doesn't. http://pastebin.com/GKXS9fYN
Specifically, the CAD places blocks until four remain, at which point the game freezes.

Crash log: http://pastebin.com/4M00hHrC
FML log: http://pastebin.com/PeQWDyGt

Still encountered against Psi-r1.1-46, all others the same.

Crash log: http://pastebin.com/UY1wwJ0r
FML log: http://pastebin.com/cPmvdeAR

two missing null -> ItemStack.EMPTY here. the setter and the return value

theoretically, you shouldn't even have to do the if (getCount == 0) set(I, EMPTY), because 0 sized stacks are automatically empty by definition.