Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at net.minecraft.server.MinecraftServer.a(SourceFile:601)
	at nn.b(SourceFile:1496)
	at ss.b(SourceFile:212)
	at nn.y(SourceFile:315)
	at nn.l_(SourceFile:278)
	at ss.l_(SourceFile:64)
	at abw.a(SourceFile:1349)
	at js.a(SourceFile:479)
	at abw.g(SourceFile:1327)

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

Time: 19-9-13 20:20
Description: Ticking entity

java.lang.NullPointerException
	at net.minecraft.server.MinecraftServer.a(SourceFile:601)
	at nn.b(SourceFile:1496)
	at ss.b(SourceFile:212)
	at nn.y(SourceFile:315)
	at nn.l_(SourceFile:278)
	at ss.l_(SourceFile:64)
	at abw.a(SourceFile:1349)
	at js.a(SourceFile:479)
	at abw.g(SourceFile:1327)
	at abw.h(SourceFile:1234)
	at js.h(SourceFile:364)
	at net.minecraft.server.MinecraftServer.t(SourceFile:471)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)


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

-- Head --
Stacktrace:
	at net.minecraft.server.MinecraftServer.a(SourceFile:601)
	at nn.b(SourceFile:1496)
	at ss.b(SourceFile:212)
	at nn.y(SourceFile:315)
	at nn.l_(SourceFile:278)
	at ss.l_(SourceFile:64)
	at abw.a(SourceFile:1349)
	at js.a(SourceFile:479)
	at abw.g(SourceFile:1327)

-- Entity being ticked --
Details:
	Entity Type: Item (ss)
	Entity ID: 125109
	Entity Name: item.item.string
	Entity's Exact location: 3,52, 56,48, 45,50
	Entity's Block location: World: (3,56,45), Chunk: (at 3,3,13 in 0,2; contains blocks 0,0,32 to 15,255,47), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Entity's Momentum: 0,29, 0,16, 0,10
Stacktrace:
	at abw.h(SourceFile:1234)
	at js.h(SourceFile:364)

-- Affected level --
Details:
	Level name: Survival 1
	All players: 1 total; [jv['u_know_who_'/277, l='Survival 1', x=3,23, y=55,00, z=45,39]]
	Chunk stats: ServerChunkCache: 488 Drop: 0
	Level seed: 6868464809491680423
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (0,0,0), Chunk: (at 0,0,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 0 game time, 0 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: ~~ERROR~~ NullPointerException: null
Stacktrace:
	at net.minecraft.server.MinecraftServer.t(SourceFile:471)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

-- System Details --
Details:
	Minecraft Version: 1.6.4
	Operating System: Mac OS X (x86_64) version 10.6.8
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 150555944 bytes (143 MB) / 324599808 bytes (309 MB) up to 1069416448 bytes (1019 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 2367 (132552 bytes; 0 MB) allocated, 1821 (101976 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 15 (840 bytes; 0 MB) allocated, 15 (840 bytes; 0 MB) used
	Player Count: 1 / 8; [jv['u_know_who_'/277, l='Survival 1', x=3,23, y=55,00, z=45,39]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.