NullPointerException on server

---- Minecraft Crash Report ----
// Ooh. Shiny.

Time: 4/24/13 12:04 PM
Description: Exception ticking world entities

java.lang.NullPointerException
	at arf.a(SourceFile:168)
	at aao.i(SourceFile:1275)
	at jb.i(SourceFile:398)
	at net.minecraft.server.MinecraftServer.r(SourceFile:470)
	at ib.r(SourceFile:258)
	at net.minecraft.server.MinecraftServer.q(SourceFile:405)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at gr.run(SourceFile:582)


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

-- Head --
Stacktrace:
	at arf.a(SourceFile:168)
	at aao.i(SourceFile:1275)
	at jb.i(SourceFile:398)

-- Affected level --
Details:
	Level name: world
	All players: 3 total; [je['Kagelye'/28909, l='world', x=-414.88, y=115.00, z=-695.35], je['minergirl1155'/43976, l='world', x=899.21, y=74.00, z=505.00], je['lucasharper8'/44037, l='world', x=15471.30, y=63.00, z=-9725.50]]
	Chunk stats: ServerChunkCache: 7154 Drop: 0
	Level seed: -6959726819361813944
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: World: (494,86,440), Chunk: (at 14,5,8 in 30,27; contains blocks 480,0,432 to 495,255,447), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 223462383 game time, 607503 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 106289 (now: false), thunder time: 41809 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.r(SourceFile:470)
	at ib.r(SourceFile:258)
	at net.minecraft.server.MinecraftServer.q(SourceFile:405)
	at net.minecraft.server.MinecraftServer.run(SourceFile:339)
	at gr.run(SourceFile:582)

-- System Details --
Details:
	Minecraft Version: 13w16b
	Operating System: Linux (amd64) version 3.2.29
	Java Version: 1.7.0_07, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 767768096 bytes (732 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB)
	JVM Flags: 3 total; -Xmx2G -Xms2G -XX:+UseG1GC
	AABB Pool Size: 3869 (216664 bytes; 0 MB) allocated, 3487 (195272 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 717 (40152 bytes; 0 MB) allocated, 537 (30072 bytes; 0 MB) used
	Player Count: 3 / 15; [je['Kagelye'/28909, l='world', x=-414.88, y=115.00, z=-695.35], je['minergirl1155'/43976, l='world', x=899.21, y=74.00, z=505.00], je['lucasharper8'/44037, l='world', x=15471.30, y=63.00, z=-9725.50]]
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)