Crash on skeleton tick.

[13:34:50] [Client thread/INFO]: Setting user: jojojonny
[13:34:50] [Client thread/INFO]: (Session ID is token:b418767b03a14939a9cfd4fa183ed2a4:f25e340fb8874be69fc65dfcb6f623ed)
[13:34:53] [Client thread/INFO]: LWJGL Version: 2.9.1
[13:34:55] [Client thread/INFO]: Reloading ResourceManager: Default
[13:34:57] [Sound Library Loader/INFO]: Sound engine started
[13:34:57] [Client thread/WARN]: File minecraft:sounds/mob/ghast/fireball.ogg does not exist, cannot add it to event minecraft:item.fireCharge.use
[13:35:03] [Client thread/INFO]: Created: 512x512 textures-atlas
[13:35:40] [Server thread/INFO]: Starting integrated minecraft server version 14w31a
[13:35:40] [Server thread/INFO]: Generating keypair
[13:35:41] [Server thread/INFO]: Preparing start region for level 0
[13:35:42] [Server thread/INFO]: Preparing spawn area: 35%
[13:35:43] [Server thread/INFO]: Preparing spawn area: 86%
[13:35:43] [Server thread/INFO]: Changing view distance to 4, from 10
[13:35:45] [Server thread/INFO]: jojojonny[local:E:bf7862fc] logged in with entity id 325 at (378.01507043476045, 69.24918707874468, 169.40798701998148)
[13:35:45] [Server thread/INFO]: jojojonny joined the game
[13:35:47] [Server thread/INFO]: Saving and pausing game...
[13:35:47] [Server thread/INFO]: Saving chunks for level 'Bread!'/Overworld
[13:35:48] [Server thread/INFO]: Saving chunks for level 'Bread!'/Nether
[13:35:48] [Server thread/INFO]: Saving chunks for level 'Bread!'/The End
[13:35:48] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 2641ms behind, skipping 52 tick(s)

Description: Ticking entity

java.lang.NullPointerException: Ticking entity
	at aay.l(SourceFile:209)
	at aay.k(SourceFile:155)
	at xl.bE(SourceFile:450)
	at xk.l(SourceFile:1430)
	at xl.l(SourceFile:316)
	at afc.l(SourceFile:39)
	at afm.l(SourceFile:151)
	at xk.j(SourceFile:1298)
	at xl.j(SourceFile:194)
	at afc.j(SourceFile:44)
	at aqh.a(SourceFile:1410)