Hopper: java.lang.NullPointerException: Exception in server tick loop

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-398233/

Crash:

java.lang.NullPointerException: Exception in server tick loop
	at na.d(SourceFile:103)
	at na.a(SourceFile:95)
	at mr.c(SourceFile:130)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	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)

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

---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 10/18/13 4:12 PM
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at na.d(SourceFile:103)
	at na.a(SourceFile:95)
	at mr.c(SourceFile:130)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	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:
---------------------------------------------------------------------------------------

-- System Details --
Details:
	Minecraft Version: 13w42b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_17, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 144499632 bytes (137 MB) / 401956864 bytes (383 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 9580 (536480 bytes; 0 MB) allocated, 9580 (536480 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 102
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1248 (69888 bytes; 0 MB) allocated, 1248 (69888 bytes; 0 MB) used
	Player Count: 1 / 8; [ml['me04'/21288, l='FunPark', x=211.77, y=64.00, z=190.11]]
	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-398233/19200217/