Total crash of Minecraft

---- Minecraft Crash Report ----

Time: 7/2/13 11:48 AM
Description: Exception in server tick loop

java.lang.NullPointerException
	at ams.<init>(SourceFile:33)
	at amr.a(SourceFile:372)
	at amr.a(SourceFile:334)
	at adm.a(SourceFile:395)
	at abr.f(SourceFile:307)
	at aim.a(SourceFile:384)
	at aim.a(SourceFile:513)
	at agd.a(SourceFile:392)
	at aio.a(SourceFile:29)
	at aii.a(SourceFile:76)
	at aeo.a(SourceFile:425)
	at jo.a(SourceFile:168)
	at adm.a(SourceFile:732)
	at jo.c(SourceFile:105)
	at jn.<init>(SourceFile:29)
	at jm.a(SourceFile:208)
	at jm.a(SourceFile:240)
	at hk.a(SourceFile:138)
	at hk.c(SourceFile:185)
	at hk.a(SourceFile:82)
	at bkr.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:488)
	at net.minecraft.server.MinecraftServer.s(SourceFile:405)
	at bko.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at hf.run(SourceFile:582)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 1.6.1
	Operating System: Mac OS X (x86_64) version 10.6.8
	Java Version: 1.6.0_37, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 57430192 bytes (54 MB) / 137773056 bytes (131 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 2092 (117152 bytes; 0 MB) allocated, 2092 (117152 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 353 (19768 bytes; 0 MB) allocated, 353 (19768 bytes; 0 MB) used
	Player Count: 1 / 8; [js['mothyl'/222, l='The Beauty', x=-434.39, y=103.77, z=535.32]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

What I expected to happen was...:
My game world should open/load.

What actually happened was...:
Minecraft alltogether crashed wihout loading the world. I just saw "downloading terrain".