Hopper: java.lang.NullPointerException: Exception ticking world

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-400152/

Crash:

java.lang.NullPointerException: Exception ticking world
	at mh.c(SourceFile:199)
	at mi.b(SourceFile:119)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// I just don't know what went wrong :(

Time: 10/18/13 1:21 PM
Description: Exception ticking world

java.lang.NullPointerException: Exception ticking world
	at mh.c(SourceFile:199)
	at mi.b(SourceFile:119)
	at net.minecraft.server.MinecraftServer.u(SourceFile:503)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsb.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kx.run(SourceFile:617)


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

-- Head --
Stacktrace:
	at mh.c(SourceFile:199)
	at mi.b(SourceFile:119)

-- Affected level --
Details:
	Level name: Bird House
	All players: 0 total; []
	Chunk stats: ServerChunkCache: 113 Drop: 113
	Level seed: -5879678688752728398
	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.u(SourceFile:503)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsb.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kx.run(SourceFile:617)

-- System Details --
Details:
	Minecraft Version: 13w42b
	Operating System: Windows XP (x86) version 5.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 196237288 bytes (187 MB) / 396759040 bytes (378 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 4100 (229600 bytes; 0 MB) allocated, 3949 (221144 bytes; 0 MB) used
	IntCache: cache: 11, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1731 (96936 bytes; 0 MB) allocated, 1716 (96096 bytes; 0 MB) used
	Player Count: 1 / 8; [ml['amymeimi'/3131, l='Bird House', x=268.00, y=61.50, z=60.00]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-400152/19160959/