pickblocking a ender dragon head crashes client

crash report

---- Minecraft Crash Report ----
// Hey, that tickles! Hehehe!

Time: 16/08/15 14:31
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at acj.a(SourceFile:401)
at yp.k(SourceFile:282)
at yq.m(SourceFile:404)
at biz.m(SourceFile:708)
at rd.r_(SourceFile:1436)
at yq.r_(SourceFile:229)
at biz.r_(SourceFile:114)
at agh.a(SourceFile:1414)
at agh.g(SourceFile:1392)
at agh.j(SourceFile:1285)
at ayy.s(SourceFile:1845)
at ayy.au(SourceFile:879)
at ayy.a(SourceFile:328)
at net.minecraft.client.main.Main.main(SourceFile:125)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:310)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:394)
at org.multimc.EntryPoint.listen(EntryPoint.java:170)
at org.multimc.EntryPoint.main(EntryPoint.java:54)

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

– Head –
Stacktrace:
at acj.a(SourceFile:401)
at yp.k(SourceFile:282)
at yq.m(SourceFile:404)
at biz.m(SourceFile:708)
at rd.r_(SourceFile:1436)
at yq.r_(SourceFile:229)
at biz.r_(SourceFile:114)
at agh.a(SourceFile:1414)
at agh.g(SourceFile:1392)

– Entity being ticked –
Details:
Entity Type: null (biz)
Entity ID: 3870
Entity Name: Stobbsie
Entity's Exact location: -918.77, 111.75, -1146.71
Entity's Block location: -919.00,111.00,-1147.00 - World: (-919,111,-1147), Chunk: (at 9,6,5 in -58,-72; contains blocks -928,0,-1152 to -913,255,-1137), Region: (-2,-3; contains chunks -64,-96 to -33,-65, blocks -1024,0,-1536 to -513,255,-1025)
Entity's Momentum: 0.04, 0.00, -0.01
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null
Stacktrace:
at agh.j(SourceFile:1285)

– Affected level –
Details:
Level name: MpServer
All players: 2 total; [biz['Stobbsie'/3870, l='MpServer', x=-918.77, y=111.75, z=-1146.71], bja['CleverPaella'/65, l='MpServer', x=-918.83, y=113.22, z=-1148.69]]
Chunk stats: MultiplayerChunkCache: 435, 435
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: 8.00,64.00,8.00 - World: (8,64,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 50869 game time, 38219 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 65 total; [xs['Endermite'/23665, l='MpServer', x=-912.50, y=114.00, z=-1167.66], xs['Endermite'/23663, l='MpServer', x=-917.69, y=115.00, z=-1174.53], xr['Enderman'/23883, l='MpServer', x=-924.50, y=58.00, z=-1179.50], bja['CleverPaella'/65, l='MpServer', x=-234.99, y=115.60, z=-1497.98], xr['Enderman'/23882, l='MpServer', x=-925.50, y=58.00, z=-1181.50], xr['Enderman'/23885, l='MpServer', x=-921.50, y=58.00, z=-1184.50], xr['Enderman'/23884, l='MpServer', x=-924.50, y=58.00, z=-1184.50], xs['Endermite'/23632, l='MpServer', x=-918.53, y=117.00, z=-1149.75], xs['Endermite'/23620, l='MpServer', x=-913.25, y=110.00, z=-1175.50], xs['Endermite'/23623, l='MpServer', x=-918.63, y=114.00, z=-1172.34], bja['CleverPaella'/65, l='MpServer', x=-918.83, y=113.22, z=-1148.69], xr['Enderman'/23607, l='MpServer', x=-908.94, y=57.00, z=-1177.06], xr['Enderman'/23383, l='MpServer', x=-894.31, y=38.00, z=-1161.31], xr['Enderman'/23864, l='MpServer', x=-984.50, y=57.00, z=-1085.50], xr['Enderman'/23866, l='MpServer', x=-984.50, y=57.00, z=-1087.50], xr['Enderman'/23860, l='MpServer', x=-973.50, y=63.00, z=-1095.50], xr['Enderman'/23861, l='MpServer', x=-970.50, y=63.00, z=-1095.50], xr['Enderman'/23862, l='MpServer', x=-973.50, y=63.00, z=-1100.50], xr['Enderman'/23863, l='MpServer', x=-975.50, y=63.00, z=-1099.50], xr['Enderman'/23856, l='MpServer', x=-852.50, y=38.00, z=-1216.50], xr['Enderman'/23584, l='MpServer', x=-863.50, y=61.00, z=-1225.50], xr['Enderman'/23822, l='MpServer', x=-943.50, y=58.00, z=-1201.50], xr['Enderman'/23821, l='MpServer', x=-941.47, y=58.00, z=-1211.22], xr['Enderman'/23820, l='MpServer', x=-941.59, y=58.00, z=-1205.44], biz['Stobbsie'/3870, l='MpServer', x=-918.77, y=111.75, z=-1146.71], xr['Enderman'/23574, l='MpServer', x=-871.50, y=58.00, z=-1216.50], xr['Enderman'/23811, l='MpServer', x=-942.50, y=58.00, z=-1191.50], xr['Enderman'/23810, l='MpServer', x=-943.50, y=58.00, z=-1188.50], xr['Enderman'/23809, l='MpServer', x=-942.53, y=58.00, z=-1197.91], xr['Enderman'/23808, l='MpServer', x=-937.50, y=58.00, z=-1192.50], xr['Enderman'/23838, l='MpServer', x=-897.50, y=58.00, z=-1186.50], xr['Enderman'/23839, l='MpServer', x=-943.50, y=58.00, z=-1190.50], xr['Enderman'/23564, l='MpServer', x=-914.31, y=41.00, z=-1153.53], bja['CleverPaella'/65, l='MpServer', x=-239.72, y=126.16, z=-1499.72], xr['Enderman'/23837, l='MpServer', x=-899.50, y=58.00, z=-1185.50], xr['Enderman'/23410, l='MpServer', x=-933.81, y=40.00, z=-1176.50], xr['Enderman'/23557, l='MpServer', x=-899.50, y=44.00, z=-1169.22], xr['Enderman'/23794, l='MpServer', x=-894.50, y=46.00, z=-1174.50], xr['Enderman'/23806, l='MpServer', x=-869.50, y=60.00, z=-1222.28], xr['Enderman'/23805, l='MpServer', x=-868.41, y=60.00, z=-1222.91], xr['Enderman'/23804, l='MpServer', x=-869.31, y=60.00, z=-1225.63], xr['Enderman'/23429, l='MpServer', x=-918.50, y=70.00, z=-1215.50], vi['Shulker'/23182, l='MpServer', x=-916.50, y=114.00, z=-1171.50], bja['CleverPaella'/65, l='MpServer', x=-330.66, y=72.34, z=-977.38], xr['Enderman'/23790, l='MpServer', x=-969.50, y=59.00, z=-1068.50], bja['CleverPaella'/65, l='MpServer', x=-238.54, y=78.66, z=-1330.29], xr['Enderman'/23788, l='MpServer', x=-972.50, y=59.00, z=-1068.50], xr['Enderman'/23444, l='MpServer', x=-917.50, y=70.00, z=-1207.50], xr['Enderman'/23223, l='MpServer', x=-919.78, y=59.00, z=-1189.66], xr['Enderman'/23473, l='MpServer', x=-918.81, y=57.00, z=-1176.25], xr['Enderman'/23474, l='MpServer', x=-905.00, y=53.00, z=-1170.56], vi['Shulker'/23017, l='MpServer', x=-897.50, y=100.00, z=-1211.50], xr['Enderman'/23497, l='MpServer', x=-896.78, y=59.00, z=-1187.50], vi['Shulker'/23008, l='MpServer', x=-898.50, y=95.00, z=-1190.50], vi['Shulker'/23009, l='MpServer', x=-895.50, y=95.00, z=-1190.50], vi['Shulker'/23010, l='MpServer', x=-915.50, y=88.00, z=-1211.50], vi['Shulker'/23011, l='MpServer', x=-910.50, y=63.00, z=-1210.50], vi['Shulker'/23012, l='MpServer', x=-910.50, y=63.00, z=-1213.50], vi['Shulker'/23013, l='MpServer', x=-902.50, y=79.00, z=-1210.50], vi['Shulker'/23014, l='MpServer', x=-902.50, y=79.00, z=-1213.50], vi['Shulker'/23015, l='MpServer', x=-899.50, y=79.00, z=-1212.50], xr['Enderman'/23518, l='MpServer', x=-933.03, y=37.00, z=-1158.31], vi['Shulker'/23007, l='MpServer', x=-916.50, y=115.00, z=-1175.50], vi['Shulker'/23006, l='MpServer', x=-920.50, y=110.00, z=-1175.50], bja['CleverPaella'/65, l='MpServer', x=-918.83, y=113.22, z=-1148.69]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Non-integrated multiplayer server
Stacktrace:
at bhb.a(SourceFile:314)
at ayy.b(SourceFile:2297)
at ayy.a(SourceFile:337)
at net.minecraft.client.main.Main.main(SourceFile:125)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:310)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:394)
at org.multimc.EntryPoint.listen(EntryPoint.java:170)
at org.multimc.EntryPoint.main(EntryPoint.java:54)

– System Details –
Details:
Minecraft Version: 15w33c
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.7.0_71, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 209653192 bytes (199 MB) / 531103744 bytes (506 MB) up to 3728211968 bytes (3555 MB)
JVM Flags: 4 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xms512m -Xmx4000m -XX:PermSize=4000m
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: MultiMC5
LWJGL: 2.9.1
OpenGL: AMD Radeon R9 200 / HD 7900 Series GL version 4.5.13399 Compatibility Profile Context 15.200.1046.2, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs:
Current Language: English (US)
Profiler Position: N/A (disabled)
CPU: 8x Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz