Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at ou.b(SourceFile:536)
	at ou.aL(SourceFile:399)
	at ou.z(SourceFile:222)
	at ov.z(SourceFile:128)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at ov.o_(SourceFile:169)
	at sd.o_(SourceFile:107)
	at act.a(SourceFile:1351)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1329)

---- Minecraft Crash Report ----
// My bad.

Time: 05/09/13 10:08 PM
Description: Ticking entity

java.lang.NullPointerException
	at ou.b(SourceFile:536)
	at ou.aL(SourceFile:399)
	at ou.z(SourceFile:222)
	at ov.z(SourceFile:128)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at ov.o_(SourceFile:169)
	at sd.o_(SourceFile:107)
	at act.a(SourceFile:1351)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1329)
	at act.h(SourceFile:1236)
	at kd.h(SourceFile:364)
	at net.minecraft.server.MinecraftServer.t(SourceFile:463)
	at net.minecraft.server.MinecraftServer.s(SourceFile:398)
	at bng.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hs.run(SourceFile:575)


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

-- Head --
Stacktrace:
	at ou.b(SourceFile:536)
	at ou.aL(SourceFile:399)
	at ou.z(SourceFile:222)
	at ov.z(SourceFile:128)
	at oc.o_(SourceFile:279)
	at ou.o_(SourceFile:1167)
	at ov.o_(SourceFile:169)
	at sd.o_(SourceFile:107)
	at act.a(SourceFile:1351)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1329)

-- Entity being ticked --
Details:
	Entity Type: Bat (sd)
	Entity ID: 287902
	Entity Name: Bat
	Entity's Exact location: -5.50, 67.00, 41.50
	Entity's Block location: World: (-6,67,41), Chunk: (at 10,4,9 in -1,2; contains blocks -16,0,32 to -1,255,47), 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:1236)
	at kd.h(SourceFile:364)

-- Affected level --
Details:
	Level name: z
	All players: 1 total; [kg['fishycheeze'/279944, l='z', x=-5.56, y=67.49, z=41.56]]
	Chunk stats: ServerChunkCache: 854 Drop: 0
	Level seed: 8246069389725888314
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: World: (-56,64,256), Chunk: (at 8,4,0 in -4,16; contains blocks -64,0,256 to -49,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 280967 game time, 31183 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 94250 (now: false), thunder time: 108444 (now: true)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.t(SourceFile:463)
	at net.minecraft.server.MinecraftServer.s(SourceFile:398)
	at bng.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hs.run(SourceFile:575)

-- System Details --
Details:
	Minecraft Version: 13w36a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 124178456 bytes (118 MB) / 873857024 bytes (833 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 238 (13328 bytes; 0 MB) allocated, 191 (10696 bytes; 0 MB) used
	Suspicious classes: [com.ibm.icu.text.ArabicShapingException], [gnu.trove.TIntCollection], [gnu.trove.impl.HashFunctions, PrimeFinder], [gnu.trove.impl.hash.THash, TPrimitiveHash, TIntIntHash], [gnu.trove.iterator.TIterator, TAdvancingIterator, TIntIntIterator], [gnu.trove.map.TIntIntMap], [gnu.trove.map.hash.TIntIntHashMap], [gnu.trove.procedure.TIntIntProcedure], [gnu.trove.set.TIntSet]
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 66 (3696 bytes; 0 MB) allocated, 41 (2296 bytes; 0 MB) used
	Player Count: 1 / 8; [kg['fishycheeze'/279944, l='z', x=-5.56, y=67.49, z=41.56]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.