Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at act.a(SourceFile:40)
	at wx.h(SourceFile:135)
	at wx.a(SourceFile:77)
	at xd.c(SourceFile:78)
	at vx.a(SourceFile:222)
	at bft.a(SourceFile:295)
	at bai.a(SourceFile:491)
	at bai.b(SourceFile:464)
	at azi.d(SourceFile:241)
	at azi.m(SourceFile:208)

---- Minecraft Crash Report ----
// This doesn't make any sense!

Time: 9/13/13 1:43 PM
Description: Updating screen events

java.lang.NullPointerException
	at act.a(SourceFile:40)
	at wx.h(SourceFile:135)
	at wx.a(SourceFile:77)
	at xd.c(SourceFile:78)
	at vx.a(SourceFile:222)
	at bft.a(SourceFile:295)
	at bai.a(SourceFile:491)
	at bai.b(SourceFile:464)
	at azi.d(SourceFile:241)
	at azi.m(SourceFile:208)
	at awo.m(SourceFile:1210)
	at awo.V(SourceFile:690)
	at awo.e(SourceFile:646)
	at net.minecraft.client.main.Main.main(SourceFile:103)


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

-- Head --
Stacktrace:
	at act.a(SourceFile:40)
	at wx.h(SourceFile:135)
	at wx.a(SourceFile:77)
	at xd.c(SourceFile:78)
	at vx.a(SourceFile:222)
	at bft.a(SourceFile:295)
	at bai.a(SourceFile:491)
	at bai.b(SourceFile:464)
	at azi.d(SourceFile:241)
	at azi.m(SourceFile:208)

-- Affected screen --
Details:
	Screen name: bbg

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bfz['TheGreenDoctor'/0, l='MpServer', x=-8.60, y=83.62, z=13.04]]
	Chunk stats: MultiplayerChunkCache: 225, 225
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-1508,4,597), Chunk: (at 12,0,5 in -95,37; contains blocks -1520,0,592 to -1505,255,607), Region: (-3,1; contains chunks -96,32 to -65,63, blocks -1536,0,512 to -1025,255,1023)
	Level time: 161432 game time, 25248 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: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 2 total; [vb['Villager'/1, l='MpServer', x=-6.50, y=82.00, z=13.50], bfz['TheGreenDoctor'/0, l='MpServer', x=-8.60, y=83.62, z=13.04]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bfu.a(SourceFile:285)
	at awo.b(SourceFile:1821)
	at awo.e(SourceFile:655)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w37b
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_13, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 174158760 bytes (166 MB) / 429785088 bytes (409 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 7955 (445480 bytes; 0 MB) allocated, 3 (168 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 13w37b
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6320 Graphics GL version 4.2.12002 Compatibility Profile Context 9.12.0.0, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 401 (22456 bytes; 0 MB) allocated, 25 (1400 bytes; 0 MB) used