Game crashes when arrow is shooten at dispenser (Intended to shoot arrows at the player) with wooden button

This log shows when it crashes:

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Ticking entity

A full error report has been saved to C:\Users\Nikolai\AppData\Roaming\.minecraft\crash-reports\crash-2012-12-18_22.10.54-server.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash :(



--- BEGIN ERROR REPORT 98d3ac24 --------
Full report at:
C:\Users\Nikolai\AppData\Roaming\.minecraft\crash-reports\crash-2012-12-18_22.10.54-server.txt
Please show that file to Mojang, NOT just this screen!

Generated 18.12.12 22:11

-- Head --
Stacktrace:
	at xp.a(SourceFile:59)
	at qz.j_(SourceFile:273)
	at yc.a(SourceFile:1319)
	at in.a(SourceFile:450)
	at yc.g(SourceFile:1297)

-- Entity being ticked --
Details:
	Entity Type: Arrow (qz)
	Entity ID: 1468
	Name: arrow
	Exact location: -141,18, 70,40, 180,71
	Block location: World: (-142,70,180), Chunk: (at 2,4,4 in -9,11; contains blocks -144,0,176 to -129,255,191), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Momentum: 0,06, -0,17, 1,07
Stacktrace:
	at yc.h(SourceFile:1196)
	at in.h(SourceFile:362)

-- Affected level --
Details:
	Level name: 1.4.6 pre
	All players: 1 total; [iq['takemori'/333, l='1.4.6 pre', x=-141,58, y=69,00, z=181,89]]
	Chunk stats: ServerChunkCache: 760 Drop: 0
	Level seed: 971367771632072719
	Level generator: ID 00 - default, ver 1. Features enabled: true
	Level generator options: 
	Level spawn location: World: (-38,64,258), Chunk: (at 10,4,2 in -3,16; contains blocks -48,0,256 to -33,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 68771 game time, 71984 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 104104 (now: false), thunder time: 9438 (now: true)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: true
Stacktrace:
	at net.minecraft.server.MinecraftServer.r(SourceFile:744)
	at net.minecraft.server.MinecraftServer.q(SourceFile:679)
	at bdz.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:613)
	at fy.run(SourceFile:849)

-- System Details --
Details:
	Minecraft Version: 1.4.6
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_01, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 276996840 bytes (264 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 5130 (287280 bytes; 0 MB) allocated, 4692 (262752 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 9, tcache: 0, allocated: 3, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1647 (92232 bytes; 0 MB) allocated, 1321 (73976 bytes; 0 MB) used
	Player Count: 1 / 8; [iq['takemori'/333, l='1.4.6 pre', x=-141,58, y=69,00, z=181,89]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

java.lang.NullPointerException
	at xp.a(SourceFile:59)
	at qz.j_(SourceFile:273)
	at yc.a(SourceFile:1319)
	at in.a(SourceFile:450)
	at yc.g(SourceFile:1297)
	at yc.h(SourceFile:1196)
	at in.h(SourceFile:362)
	at net.minecraft.server.MinecraftServer.r(SourceFile:744)
	at net.minecraft.server.MinecraftServer.q(SourceFile:679)
	at bdz.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:613)
	at fy.run(SourceFile:849)
--- END ERROR REPORT 876d6578 ----------