Chests empty, error in console

[starg09]

This error appears every time someone interacts with a chest. We're on the latest Protocol Hack before Spigot 1.8, but this bug has been there for some time (I just forgot to submit it)

http://paste.ee/p/q2SvP

Basically, there's a slight chance it doesn't happen on the first few chest on the match, and thos have perfect loot, in random values. But if this error shows up (which it uses to), then the chests opened after that are always empty... Could you help us please?