Hopper: java.lang.NullPointerException: Ticking entity

java.lang.NullPointerException: Ticking entity
	at aht.E(SourceFile:192)
	at aht.c(SourceFile:198)
	at sw.e(SourceFile:112)
	at su.m_(SourceFile:94)
	at aht.a(SourceFile:1370)
	at nr.a(SourceFile:528)
	at aht.g(SourceFile:1348)

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

Time: 31/01/14 16:15
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
	at aht.E(SourceFile:192)
	at aht.c(SourceFile:198)
	at sw.e(SourceFile:112)
	at su.m_(SourceFile:94)
	at aht.a(SourceFile:1370)
	at nr.a(SourceFile:528)
	at aht.g(SourceFile:1348)
	at aht.i(SourceFile:1253)
	at nr.i(SourceFile:401)
	at net.minecraft.server.MinecraftServer.v(SourceFile:527)
	at net.minecraft.server.MinecraftServer.u(SourceFile:461)
	at cae.u(SourceFile:123)
	at net.minecraft.server.MinecraftServer.run(SourceFile:377)
	at mh.run(SourceFile:647)


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

-- Head --
Stacktrace:
	at aht.E(SourceFile:192)
	at aht.c(SourceFile:198)
	at sw.e(SourceFile:112)
	at su.m_(SourceFile:94)
	at aht.a(SourceFile:1370)
	at nr.a(SourceFile:528)
	at aht.g(SourceFile:1348)

-- Entity being ticked --
Details:
	Entity Type: LeashKnot (sw)
	Entity ID: 434798
	Entity Name: entity.LeashKnot.name
	Entity's Exact location: -1400.50, 56.00, 1007.50
	Entity's Block location: -1401.00,56.00,1007.00 - World: (-1401,56,1007), Chunk: (at 7,3,15 in -88,62; contains blocks -1408,0,992 to -1393,255,1007), Region: (-3,1; contains chunks -96,32 to -65,63, blocks -1536,0,512 to -1025,255,1023)
	Entity's Momentum: 0.00, 0.00, 0.00
	Entity's Rider: ~~ERROR~~ NullPointerException: null
	Entity's Vehicle: ~~ERROR~~ NullPointerException: null
Stacktrace:
	at aht.i(SourceFile:1253)
	at nr.i(SourceFile:401)

-- Affected level --
Details:
	Level name: Tutorial World
	All players: 1 total; [nu['_netherpig_'/592, l='Tutorial World', x=-1399.22, y=56.00, z=1008.97]]
	Chunk stats: ServerChunkCache: 462 Drop: 0
	Level seed: 1271853379575527447
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 2;7,3x1,52x24;2;
	Level spawn location: -1384.00,4.00,970.00 - World: (-1384,4,970), Chunk: (at 8,0,10 in -87,60; contains blocks -1392,0,960 to -1377,255,975), Region: (-3,1; contains chunks -96,32 to -65,63, blocks -1536,0,512 to -1025,255,1023)
	Level time: 154631 game time, 5000 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 10134 (now: true), thunder time: 16457 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.v(SourceFile:527)
	at net.minecraft.server.MinecraftServer.u(SourceFile:461)
	at cae.u(SourceFile:123)
	at net.minecraft.server.MinecraftServer.run(SourceFile:377)
	at mh.run(SourceFile:647)

-- System Details --
Details:
	Minecraft Version: 14w05b
	Operating System: Windows 8 (amd64) version 6.2
	Java Version: 1.7.0_21, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 149273416 bytes (142 MB) / 573636608 bytes (547 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Player Count: 1 / 8; [nu['_netherpig_'/592, l='Tutorial World', x=-1399.22, y=56.00, z=1008.97]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.