Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at bcw.a(SourceFile:861)
	at ge.a(SourceFile:51)
	at co.b(SourceFile:354)
	at bcw.e(SourceFile:98)
	at bdd.b(SourceFile:60)

---- Minecraft Crash Report ----
// I just don't know what went wrong :(

Time: 10/2/13 3:16 PM
Description: Exception in world tick

java.lang.NullPointerException
	at bcw.a(SourceFile:861)
	at ge.a(SourceFile:51)
	at co.b(SourceFile:354)
	at bcw.e(SourceFile:98)
	at bdd.b(SourceFile:60)
	at atv.k(SourceFile:1386)
	at atv.S(SourceFile:663)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at bcw.a(SourceFile:861)
	at ge.a(SourceFile:51)
	at co.b(SourceFile:354)
	at bcw.e(SourceFile:98)
	at bdd.b(SourceFile:60)

-- Affected level --
Details:
	Problem: Level is null!
Stacktrace:
	at atv.k(SourceFile:1386)
	at atv.S(SourceFile:663)
	at atv.d(SourceFile:619)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.6.0_15, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
	Memory: 330928784 bytes (315 MB) / 528809984 bytes (504 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 149383 (8365448 bytes; 7 MB) allocated, 844 (47264 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Launched Version: 1.6.4
	LWJGL: 2.9.0
	OpenGL: Mobile Intel(R) 4 Series Express Chipset Family GL version 2.1.0 - Build 8.15.10.1883, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null