on 1.7.2 i press play and the game crashes

Put the summary of the bug you're having here

What I expected to happen was...:
to go to the homescreen and start my world and hopefully get mods and maps.

What actually happened was...:
I pressed play and it crashed so I pressed report mojang

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
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