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

java.lang.NullPointerException: Exception in server tick loop
	at axn.f(SourceFile:202)
	at lm.m(SourceFile:691)
	at net.minecraft.server.MinecraftServer.a(SourceFile:909)
	at btq.a(SourceFile:196)
	at qf.b(SourceFile:97)
	at net.minecraft.server.MinecraftServer.u(SourceFile:476)
	at btq.u(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:359)
	at lh.run(SourceFile:618)

---- Minecraft Crash Report ----
// I feel sad now :(

Time: 26.02.14 11:31
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at axn.f(SourceFile:202)
	at lm.m(SourceFile:691)
	at net.minecraft.server.MinecraftServer.a(SourceFile:909)
	at btq.a(SourceFile:196)
	at qf.b(SourceFile:97)
	at net.minecraft.server.MinecraftServer.u(SourceFile:476)
	at btq.u(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:359)
	at lh.run(SourceFile:618)


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: 1.7.5
	Operating System: Windows XP (x86) version 5.1
	Java Version: 1.7.0_51, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 98641224 bytes (94 MB) / 308772864 bytes (294 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Player Count: 1 / 8; [mv['Player'/52, l='Demo_World', x=-202,18, y=64,00, z=-191,47]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.