Null Pointer Exception?

I've been running this server for a while, and decided to give the snapshots a whirl again...

Whenever a player logs in, they connect properly but are then disconnected while downloading terrain. I've attached a text file with the relevant parts of the server log.

I started the server in 12w13b, and the error happened.
Then, upon hearing of a more recent version I tried it and it still happened.

Due to it being a log-in crash, I've removed the gamemode field for its irrelevancy.