Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at ny.a(SourceFile:89)
	at ou.aL(SourceFile:396)
	at ou.z(SourceFile:222)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at uw.o_(SourceFile:204)
	at bfn.o_(SourceFile:49)
	at act.a(SourceFile:1365)
	at act.g(SourceFile:1343)

---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 6-9-13 15:05
Description: Ticking entity

java.lang.NullPointerException
	at ny.a(SourceFile:89)
	at ou.aL(SourceFile:396)
	at ou.z(SourceFile:222)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at uw.o_(SourceFile:204)
	at bfn.o_(SourceFile:49)
	at act.a(SourceFile:1365)
	at act.g(SourceFile:1343)
	at act.h(SourceFile:1250)
	at awb.m(SourceFile:1426)
	at awb.V(SourceFile:686)
	at awb.e(SourceFile:642)
	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 ny.a(SourceFile:89)
	at ou.aL(SourceFile:396)
	at ou.z(SourceFile:222)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at uw.o_(SourceFile:204)
	at bfn.o_(SourceFile:49)
	at act.a(SourceFile:1365)
	at act.g(SourceFile:1343)

-- Entity being ticked --
Details:
	Entity Type: null (bfn)
	Entity ID: 1598
	Entity Name: sgs1996
	Entity's Exact location: -28,30, 67,62, 256,70
	Entity's Block location: World: (-29,67,256), Chunk: (at 3,4,0 in -2,16; contains blocks -32,0,256 to -17,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Entity's Momentum: 0,00, 0,00, 0,00
Stacktrace:
	at act.h(SourceFile:1250)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bfn['sgs1996'/1598, l='MpServer', x=-28,30, y=67,62, z=256,70]]
	Chunk stats: MultiplayerChunkCache: 0, 0
	Level seed: 0
	Level generator: ID 02 - largeBiomes, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (220,64,256), Chunk: (at 12,4,0 in 13,16; contains blocks 208,0,256 to 223,255,271), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 7819 game time, 7819 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: 1 total; [bfn['sgs1996'/1598, l='MpServer', x=-28,30, y=67,62, z=256,70]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bfi.a(SourceFile:285)
	at awb.b(SourceFile:1813)
	at awb.e(SourceFile:651)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w36b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 56296928 bytes (53 MB) / 191844352 bytes (182 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 6 (336 bytes; 0 MB) allocated, 5 (280 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 102
	Launched Version: 13w36b
	LWJGL: 2.9.0
	OpenGL: AMD RADEON HD 6450 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: 54 (3024 bytes; 0 MB) allocated, 14 (784 bytes; 0 MB) used