Hopper: java.lang.NullPointerException 13w37a

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-139291/

Crash:

java.lang.NullPointerException
	at dz.b(SourceFile:116)
	at dz.a(SourceFile:41)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 12.09.13 19:25
Description: Sending packet

java.lang.NullPointerException
	at dz.b(SourceFile:116)
	at dz.a(SourceFile:41)
	at kt.b(SourceFile:430)
	at lm.b(SourceFile:170)
	at jf.a(SourceFile:86)
	at bnz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.u(SourceFile:482)
	at net.minecraft.server.MinecraftServer.t(SourceFile:399)
	at bnw.t(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:333)
	at ja.run(SourceFile:576)


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

-- Head --
Stacktrace:
	at dz.b(SourceFile:116)
	at dz.a(SourceFile:41)

-- Packet being sent --
Details:
	Packet ID: 200
	Packet class: fb
Stacktrace:
	at kt.b(SourceFile:430)
	at lm.b(SourceFile:170)
	at jf.a(SourceFile:86)
	at bnz.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.u(SourceFile:482)
	at net.minecraft.server.MinecraftServer.t(SourceFile:399)
	at bnw.t(SourceFile:124)
	at net.minecraft.server.MinecraftServer.run(SourceFile:333)
	at ja.run(SourceFile:576)

-- System Details --
Details:
	Minecraft Version: 13w37a
	Operating System: Mac OS X (x86_64) version 10.8.4
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 133041896 bytes (126 MB) / 297111552 bytes (283 MB) up to 2138767360 bytes (2039 MB)
	JVM Flags: 1 total; -Xmx2G
	AABB Pool Size: 2559 (143304 bytes; 0 MB) allocated, 2559 (143304 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 154 (8624 bytes; 0 MB) allocated, 146 (8176 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.

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-139291/10230951/