Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at acd.<init>(SourceFile:90)
	at atv.a(SourceFile:1426)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)

---- Minecraft Crash Report ----
// Sorry :(

Time: 9/21/13 3:54 PM
Description: Updating screen events

java.lang.NullPointerException
	at acd.<init>(SourceFile:90)
	at atv.a(SourceFile:1426)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)
	at atv.k(SourceFile:1158)
	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 acd.<init>(SourceFile:90)
	at atv.a(SourceFile:1426)
	at awh.e(SourceFile:157)
	at awh.a(SourceFile:122)
	at awe.a(SourceFile:69)
	at awe.d(SourceFile:128)
	at awe.m(SourceFile:107)

-- Affected screen --
Details:
	Screen name: blt
Stacktrace:
	at atv.k(SourceFile:1158)
	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: Mac OS X (x86_64) version 10.8.4
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 64119600 bytes (61 MB) / 94572544 bytes (90 MB) up to 1065025536 bytes (1015 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 1.6.4
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6770M OpenGL Engine GL version 2.1 ATI-1.8.18, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Current Language: English (UK)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null