Minecraft crashes while staying in the Main Menu, and leaving it unattended for a few hours.

What was I doing: I was busy doing some VM maintenience while leaving Minecraft running in the main menu. At the time just before the crash, the background music is playing.

How I know the crash occurred: When the background music stops playing abruptedly.

Any way to reproduce it reliably? No idea. It rarely occurs that the crash happened in the Main Menu, with the music playing nicely.

Crash log:

=================== CRASH LOG BELOW ====================

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Unexpected error
This error has been saved to C:\Users\Thompson\AppData\Roaming\.minecraft\crash-reports\crash-2012-11-06_23.11.49-client.txt for your convenience. Please include a copy of this file if you report this crash to anyone.



--- BEGIN ERROR REPORT f69b98b1 --------
Generated 11/6/12 11:11 PM

- Minecraft Version: 1.4.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_07, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 453098600 bytes (432 MB) / 520683520 bytes (496 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- AABB Pool Size: 13 (728 bytes; 0 MB) allocated, 11 (616 bytes; 0 MB) used
- LWJGL: 2.4.2
- OpenGL: GeForce GTS 250/PCIe/SSE2 GL version 3.3.0, NVIDIA Corporation
- Is Modded: Probably not
- Type: Client
- Texture Pack: Default
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: ~ERROR~ NullPointerException: null

java.lang.NullPointerException
	at aud.b(SourceFile:256)
	at net.minecraft.client.Minecraft.a(SourceFile:433)
	at awr.a(SourceFile:484)
	at db.a(SourceFile:27)
	at bx.b(SourceFile:341)
	at awr.d(SourceFile:98)
	at awz.b(SourceFile:61)
	at net.minecraft.client.Minecraft.l(SourceFile:1282)
	at net.minecraft.client.Minecraft.J(SourceFile:582)
	at net.minecraft.client.Minecraft.run(SourceFile:534)
	at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 4f0e61e3 ----------

============= END CRASH LOG ========================