Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at aiv.a(SourceFile:36)
	at ain.a(SourceFile:87)
	at aet.a(SourceFile:426)
	at jr.a(SourceFile:168)
	at adr.a(SourceFile:732)
	at jr.c(SourceFile:105)
	at jq.<init>(SourceFile:29)
	at jp.a(SourceFile:208)
	at jp.a(SourceFile:240)
	at hn.a(SourceFile:141)
	at hn.c(SourceFile:188)
	at hn.a(SourceFile:85)
	at blc.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)

---- Minecraft Crash Report ----
// Oops.

Time: 10/12/13 9:57 PM
Description: Exception in server tick loop

java.lang.NullPointerException
	at aiv.a(SourceFile:36)
	at ain.a(SourceFile:87)
	at aet.a(SourceFile:426)
	at jr.a(SourceFile:168)
	at adr.a(SourceFile:732)
	at jr.c(SourceFile:105)
	at jq.<init>(SourceFile:29)
	at jp.a(SourceFile:208)
	at jp.a(SourceFile:240)
	at hn.a(SourceFile:141)
	at hn.c(SourceFile:188)
	at hn.a(SourceFile:85)
	at blc.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.t(SourceFile:489)
	at net.minecraft.server.MinecraftServer.s(SourceFile:406)
	at bkz.s(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:340)
	at hi.run(SourceFile:583)


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: 1.6.4
	Operating System: Windows 8 (x86) version 6.2
	Java Version: 1.7.0_40, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 118142744 bytes (112 MB) / 225132544 bytes (214 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 696 (38976 bytes; 0 MB) allocated, 696 (38976 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 147 (8232 bytes; 0 MB) allocated, 147 (8232 bytes; 0 MB) used
	Player Count: 1 / 8; [jv['olivier2231'/87, l='the 4:20 world', x=714.64, y=64.00, z=-192.41]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.