[MC-35787] Application crash when pressing volume control in 13w42a

Application crashes when the user changes the friendly mobs volume control.

throws null pointer exception.

Environment

windows 7 64 bit, java 1.7_11

confirmed
1: music & sound
2: hostile mobs -> touch slider -> crash

Confirmed. Every time when I try to adjust the volume level for friendly mobs, the game crashes.

Confirmed. Happens to me too.

Confirmed, same error when clicking on the Blocks volume slider.