Because it sends a ChatComponentTranslation with a null key (from CommandRefinedRelocation.getCommandUsage) which crashes when finding formats in it.

Can I have some more info? I need a MC version and preferably a crash log.

MC Version: 1.7.2
Crash log: https://gist.github.com/CoderPuppy/b4f0a1531114d91b5318

The log isn't that helpful though because it crashes the client when trying to localize null