Hopper: java.lang.NullPointerException: Exception generating new chunk

java.lang.NullPointerException: Exception generating new chunk
	at apk.a(SourceFile:165)
	at apk.d(SourceFile:195)

---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 23/10/13 15:55
Description: Exception generating new chunk

java.lang.NullPointerException: Exception generating new chunk
	at apk.a(SourceFile:165)
	at apk.d(SourceFile:195)
	at mh.c(SourceFile:78)
	at mg.<init>(SourceFile:31)
	at mf.a(SourceFile:212)
	at mf.d(SourceFile:346)
	at lc.d(SourceFile:215)
	at mw.a(SourceFile:280)
	at iq.a(SourceFile:137)
	at is.a(SourceFile:20)
	at ef.a(SourceFile:143)
	at mr.c(SourceFile:134)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsi.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kx.run(SourceFile:617)


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

-- Head --
Stacktrace:
	at apk.a(SourceFile:165)
	at apk.d(SourceFile:195)

-- Chunk to be generated --
Details:
	Location: -24,12
	Position hash: 55834574824
	Generator: RandomLevelSource
Stacktrace:
	at mh.c(SourceFile:78)
	at mg.<init>(SourceFile:31)
	at mf.a(SourceFile:212)
	at mf.d(SourceFile:346)
	at lc.d(SourceFile:215)
	at mw.a(SourceFile:280)
	at iq.a(SourceFile:137)
	at is.a(SourceFile:20)
	at ef.a(SourceFile:143)

-- Ticking connection --
Details:
	Connection: ef@c63720
Stacktrace:
	at mr.c(SourceFile:134)
	at net.minecraft.server.MinecraftServer.u(SourceFile:529)
	at net.minecraft.server.MinecraftServer.t(SourceFile:441)
	at bsi.t(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kx.run(SourceFile:617)

-- System Details --
Details:
	Minecraft Version: 1.7.1
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 104404760 bytes (99 MB) / 518979584 bytes (494 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M
	AABB Pool Size: 7033 (393848 bytes; 0 MB) allocated, 1950 (109200 bytes; 0 MB) used
	IntCache: cache: 7, tcache: 26, allocated: 14, tallocated: 126
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1337 (74872 bytes; 0 MB) allocated, 580 (32480 bytes; 0 MB) used
	Player Count: 1 / 8; [ml['Jeff8577'/103851, l='New World 2', x=-209.44, y=86.04, z=285.62]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.