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

java.lang.NullPointerException: Exception in server tick loop
	at mu.d(SourceFile:103)
	at mu.a(SourceFile:95)
	at ml.c(SourceFile:130)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at brh.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kt.run(SourceFile:617)

---- Minecraft Crash Report ----
// Ouch. That hurt :(

Time: 11/10/13 23:38
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at mu.d(SourceFile:103)
	at mu.a(SourceFile:95)
	at ml.c(SourceFile:130)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at brh.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kt.run(SourceFile:617)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 13w41b
	Operating System: Windows 8 (x86) version 6.2
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 160114856 bytes (152 MB) / 425676800 bytes (405 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 4008 (224448 bytes; 0 MB) allocated, 3754 (210224 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 2508 (140448 bytes; 0 MB) allocated, 2256 (126336 bytes; 0 MB) used
	Player Count: 1 / 8; [mf['Gaubru'/138, l='Multi', x=388,88, y=68,00, z=-2628,21]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.