Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at java.util.HashMap.clear(Unknown Source)
	at java.util.HashSet.clear(Unknown Source)
	at ki.b(SourceFile:224)
	at ki.a(SourceFile:161)
	at jx.a(SourceFile:125)
	at net.minecraft.server.MinecraftServer.t(SourceFile:471)
	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 ----
// Oh - I know what I did wrong!

Time: 6/09/13 03:58 PM
Description: Exception in server tick loop

java.lang.NullPointerException
	at java.util.HashMap.clear(Unknown Source)
	at java.util.HashSet.clear(Unknown Source)
	at ki.b(SourceFile:224)
	at ki.a(SourceFile:161)
	at jx.a(SourceFile:125)
	at net.minecraft.server.MinecraftServer.t(SourceFile:471)
	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 8 (amd64) version 6.2
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 412137368 bytes (393 MB) / 700055552 bytes (667 MB) up to 4772200448 bytes (4551 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx5G
	AABB Pool Size: 3067 (171752 bytes; 0 MB) allocated, 2874 (160944 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: 1824 (102144 bytes; 0 MB) allocated, 1293 (72408 bytes; 0 MB) used
	Player Count: 1 / 8; [kg['ponki3'/293, l='Nuevo Mundo', x=133.95, y=65.86, z=-647.59]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.