Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at hx.a(SourceFile:164)
	at hx.a(SourceFile:59)
	at bnj.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:481)
	at net.minecraft.server.MinecraftServer.s(SourceFile:398)
	at bng.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hs.run(SourceFile:575)

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

Time: 06/09/13 16:39
Description: Exception in server tick loop

java.lang.NullPointerException
	at hx.a(SourceFile:164)
	at hx.a(SourceFile:59)
	at bnj.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:481)
	at net.minecraft.server.MinecraftServer.s(SourceFile:398)
	at bng.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:332)
	at hs.run(SourceFile:575)


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

-- System Details --
Details:
	Minecraft Version: 13w36a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 130409464 bytes (124 MB) / 243269632 bytes (232 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 288 (16128 bytes; 0 MB) allocated, 279 (15624 bytes; 0 MB) used
	Suspicious classes: [com.ibm.icu.text.ArabicShapingException], [gnu.trove.TIntCollection], [gnu.trove.impl.HashFunctions, PrimeFinder], [gnu.trove.impl.hash.THash, TPrimitiveHash, TIntIntHash], [gnu.trove.iterator.TIterator, TAdvancingIterator, TIntIntIterator], [gnu.trove.map.TIntIntMap], [gnu.trove.map.hash.TIntIntHashMap], [gnu.trove.procedure.TIntIntProcedure], [gnu.trove.set.TIntSet]
	IntCache: cache: 1, tcache: 1, allocated: 12, tallocated: 94
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 245 (13720 bytes; 0 MB) allocated, 206 (11536 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.