NPE when opening 13w16a to 13w26a：Initializing game failed

When I open 1.6.1 snapshots,crashes

Steps to Reproduce:

1.Open a version between 13w16a to 13w26a normally

2.Before the window appear,you'll be gived a message:GAME CRASHED

Observed Results:

Before the window appear,you'll be gived a message:GAME CRASHED

Expected Results:

Game starts properly