I was in the nether mining a peice of nether quartz and then my Iron pickaxe breaks then my game crashes
log:
Minecraft has crashed!
----------------------

Minecraft has stopped running because it encountered a problem; Unexpected error

A full error report has been saved to C:\Users\Thomas\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-21_14.07.40-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash

— BEGIN ERROR REPORT 62702c4f --------
Full report at:
C:\Users\Thomas\AppData\Roaming\.minecraft\crash-reports\crash-2013-01-21_14.07.40-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 1/21/13 2:07 PM

– Head –
Stacktrace:
at bbp.a(SourceFile:200)
at bbp.c(SourceFile:151)
at net.minecraft.client.Minecraft.a(SourceFile:930)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bbt['creeperbros'/200, l='MpServer', x=151.12, y=58.87, z=-317.36]]
Chunk stats: MultiplayerChunkCache: 441
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (8,64,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 1034211 game time, 1342032 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Forced entities: 2 total; [bbt['creeperbros'/200, l='MpServer', x=151.12, y=58.87, z=-317.36], qi['item.tile.hellrock'/154492, l='MpServer', x=149.54, y=57.64, z=-317.85]]
Retry entities: 0 total; []
Stacktrace:
at bbq.a(SourceFile:281)
at net.minecraft.client.Minecraft.b(SourceFile:1865)
at net.minecraft.client.Minecraft.run(SourceFile:539)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 13w03a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_12-ea, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 78040656 bytes (74 MB) / 326238208 bytes (311 MB) up to 326238208 bytes (311 MB)
JVM Flags: 2 total; -Xms350m -Xmx350m
AABB Pool Size: 3292 (184352 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
LWJGL: 2.8.4
OpenGL: Intel(R) HD Graphics 3000 GL version 3.1.0 - Build 8.15.10.2761, Intel
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: 1600 (89600 bytes; 0 MB) allocated, 15 (840 bytes; 0 MB) used

java.lang.NullPointerException
at bbp.a(SourceFile:200)
at bbp.c(SourceFile:151)
at net.minecraft.client.Minecraft.a(SourceFile:930)
at net.minecraft.client.Minecraft.l(SourceFile:1299)
at net.minecraft.client.Minecraft.K(SourceFile:573)
at net.minecraft.client.Minecraft.run(SourceFile:525)
at java.lang.Thread.run(Unknown Source)
— END ERROR REPORT 1f036cc1 ----------