Ya, looks like nobody really cares about reputation. The vanilla code would never of worked.
As it checks the world is not null before it looks up the player name from the UUID {as it needs to because the server olds that lookup}
It's not a simple fix as all the public API for that class use the players name as a string, instead of the UUID or profile or anything.
Edit:
I've pushed a fix to Forge for this: https://github.com/MinecraftForge/MinecraftForge/commit/72937c90be8a337190964e43281d3da85c43319b