Not able to join LAN worlds

I can't let my any players to join my LAN world. In any snapshots later than 14w21b.
It says "Connection error: java.lang.NullPointerException"

Steps to Reproduce:
1. Open a world, and open it to LAN
2. Ask another player to join the world.
3. You can see the option in Multiplayer, but when you click it, the connection error happens.