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

java.lang.NullPointerException: Exception in server tick loop
	at axc.f(SourceFile:202)
	at ld.m(SourceFile:690)
	at net.minecraft.server.MinecraftServer.a(SourceFile:908)
	at bsk.a(SourceFile:186)
	at pv.b(SourceFile:92)
	at net.minecraft.server.MinecraftServer.t(SourceFile:474)
	at bsk.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at ky.run(SourceFile:617)

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

Time: 25/10/13 14:23
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at axc.f(SourceFile:202)
	at ld.m(SourceFile:690)
	at net.minecraft.server.MinecraftServer.a(SourceFile:908)
	at bsk.a(SourceFile:186)
	at pv.b(SourceFile:92)
	at net.minecraft.server.MinecraftServer.t(SourceFile:474)
	at bsk.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at ky.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: 1.7.2
	Operating System: Windows 8 (x86) version 6.2
	Java Version: 1.7.0_10, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 104352384 bytes (99 MB) / 310280192 bytes (295 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 12458 (697648 bytes; 0 MB) allocated, 743 (41608 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1980 (110880 bytes; 0 MB) allocated, 104 (5824 bytes; 0 MB) used
	Player Count: 0 / 8; []
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.