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 uj.o_(SourceFile:81)
	at act.a(SourceFile:1365)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1343)

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 9/6/13 7:18 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 uj.o_(SourceFile:81)
	at act.a(SourceFile:1365)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1343)
	at act.h(SourceFile:1250)
	at kd.h(SourceFile:364)
	at net.minecraft.server.MinecraftServer.t(SourceFile:463)
	at net.minecraft.server.MinecraftServer.s(SourceFile:398)
	at bnn.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hr.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 uj.o_(SourceFile:81)
	at act.a(SourceFile:1365)
	at kd.a(SourceFile:479)
	at act.g(SourceFile:1343)

-- Entity being ticked --
Details:
	Entity Type: Slime (uj)
	Entity ID: 344
	Entity Name: Slime
	Entity's Exact location: -1423.50, 156.50, -106.50
	Entity's Block location: World: (-1424,156,-107), Chunk: (at 0,9,5 in -89,-7; contains blocks -1424,0,-112 to -1409,255,-97), Region: (-3,-1; contains chunks -96,-32 to -65,-1, blocks -1536,0,-512 to -1025,255,-1)
	Entity's Momentum: 0.00, 0.00, 0.00
Stacktrace:
	at act.h(SourceFile:1250)
	at kd.h(SourceFile:364)

-- Affected level --
Details:
	Level name: Skylands - TheKidMenace - World
	All players: 1 total; [kg['TheKidMenace'/0, l='Skylands - TheKidMenace - World', x=-1412.34, y=156.29, z=-108.30]]
	Chunk stats: ServerChunkCache: 1066 Drop: 0
	Level seed: 63780079961222836
	Level generator: ID 01 - flat, ver 0. Features enabled: true
	Level generator options: 2;50x0;1;village
	Level spawn location: World: (-1607,4,-491), Chunk: (at 9,0,5 in -101,-31; contains blocks -1616,0,-496 to -1601,255,-481), Region: (-4,-1; contains chunks -128,-32 to -97,-1, blocks -2048,0,-512 to -1537,255,-1)
	Level time: 568860 game time, 0 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 19722663 (now: false), thunder time: 19722663 (now: false)
	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 bnn.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hr.run(SourceFile:575)

-- 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), Oracle Corporation
	Memory: 65023520 bytes (62 MB) / 337477632 bytes (321 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 1852 (103712 bytes; 0 MB) allocated, 253 (14168 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 166 (9296 bytes; 0 MB) allocated, 55 (3080 bytes; 0 MB) used
	Player Count: 1 / 8; [kg['TheKidMenace'/0, l='Skylands - TheKidMenace - World', x=-1412.34, y=156.29, z=-108.30]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.