Minecraft server often crashes on 14w31a

My server often crashes after i updated to the latest snapshot. It`s not overloaded or anything because it`s just me and my friend on it. It might have something to do with the zombies trying to get to my villagers that are in a fenced of area because that is when most of the crashes happened.

The full crash report is below.

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

Time: 7/31/14 11:49 PM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
	at bou.a(SourceFile:77)
	at bou.a(SourceFile:65)
	at boy.a(SourceFile:77)
	at boy.a(SourceFile:37)
	at boy.a(SourceFile:22)
	at aay.a(SourceFile:97)
	at zj.a(SourceFile:49)
	at zb.a(SourceFile:72)
	at xl.bE(SourceFile:446)
	at xk.l(SourceFile:1430)
	at xl.l(SourceFile:316)
	at afc.l(SourceFile:39)
	at afz.l(SourceFile:203)
	at xk.j(SourceFile:1298)
	at xl.j(SourceFile:194)
	at afc.j(SourceFile:44)
	at afz.j(SourceFile:259)
	at aqh.a(SourceFile:1410)
	at qo.a(SourceFile:601)
	at aqh.g(SourceFile:1388)
	at aqh.i(SourceFile:1281)
	at qo.i(SourceFile:479)
	at net.minecraft.server.MinecraftServer.y(SourceFile:606)
	at pk.y(SourceFile:303)
	at net.minecraft.server.MinecraftServer.x(SourceFile:530)
	at net.minecraft.server.MinecraftServer.run(SourceFile:446)
	at java.lang.Thread.run(Unknown Source)


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

-- Head --
Stacktrace:
	at bou.a(SourceFile:77)
	at bou.a(SourceFile:65)
	at boy.a(SourceFile:77)
	at boy.a(SourceFile:37)
	at boy.a(SourceFile:22)
	at aay.a(SourceFile:97)
	at zj.a(SourceFile:49)
	at zb.a(SourceFile:72)
	at xl.bE(SourceFile:446)
	at xk.l(SourceFile:1430)
	at xl.l(SourceFile:316)
	at afc.l(SourceFile:39)
	at afz.l(SourceFile:203)
	at xk.j(SourceFile:1298)
	at xl.j(SourceFile:194)
	at afc.j(SourceFile:44)
	at afz.j(SourceFile:259)
	at aqh.a(SourceFile:1410)
	at qo.a(SourceFile:601)
	at aqh.g(SourceFile:1388)

-- Entity being ticked --
Details:
	Entity Type: Zombie (afz)
	Entity ID: 57
	Entity Name: Zombie
	Entity's Exact location: -357.12, 68.00, 50.23
	Entity's Block location: -358.00,68.00,50.00 - World: (-358,68,50), Chunk: (at 10,4,2 in -23,3; contains blocks -368,0,48 to -353,255,63), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Entity's Momentum: 0.00, -0.08, 0.00
	Entity's Rider: ~~ERROR~~ NullPointerException: null
	Entity's Vehicle: ~~ERROR~~ NullPointerException: null
Stacktrace:
	at aqh.i(SourceFile:1281)
	at qo.i(SourceFile:479)

-- Affected level --
Details:
	Level name: world
	All players: 1 total; [qr['kuagalaga'/193, l='world', x=-357.97, y=68.00, z=51.28]]
	Chunk stats: ServerChunkCache: 741 Drop: 0
	Level seed: -5635311526099537370
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: -268.00,64.00,21.00 - World: (-268,64,21), Chunk: (at 4,4,5 in -17,1; contains blocks -272,0,16 to -257,255,31), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 1739166 game time, 1987895 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 118871 (now: false), thunder time: 132781 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
	at net.minecraft.server.MinecraftServer.y(SourceFile:606)
	at pk.y(SourceFile:303)
	at net.minecraft.server.MinecraftServer.x(SourceFile:530)
	at net.minecraft.server.MinecraftServer.run(SourceFile:446)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 14w31a
	Operating System: Windows 8.1 (amd64) version 6.3
	Java Version: 1.8.0_11, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 827275464 bytes (788 MB) / 1029177344 bytes (981 MB) up to 1029177344 bytes (981 MB)
	JVM Flags: 2 total; -Xmx1024M -Xms1024M
	IntCache: cache: 13, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Player Count: 1 / 5; [qr['kuagalaga'/193, l='world', x=-357.97, y=68.00, z=51.28]]
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)