Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at bcw.a(SourceFile:469)
	at gg.a(SourceFile:44)
	at co.b(SourceFile:354)
	at bcw.e(SourceFile:98)
	at bdd.b(SourceFile:60)

---- Minecraft Crash Report ----
// Why is it breaking :(

Time: 30.09.13 19:10
Description: Exception in world tick

java.lang.NullPointerException
	at bcw.a(SourceFile:469)
	at gg.a(SourceFile:44)
	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:469)
	at gg.a(SourceFile:44)
	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: Linux (amd64) version 3.8.0-30-generic
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 146643128 bytes (139 MB) / 216006656 bytes (206 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 1296 (72576 bytes; 0 MB) allocated, 476 (26656 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: GeForce GTX 460 SE/PCIe/SSE2 GL version 4.3.0 NVIDIA 313.30, NVIDIA Corporation
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: Polski (Polska)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null