Hopper: java.lang.NullPointerException

java.lang.NullPointerException
	at axf.<init>(SourceFile:18)
	at axb.a(SourceFile:62)

---- Minecraft Crash Report ----
// Hi. I'm Minecraft, and I'm a crashaholic.

Time: 06/09/13 15.28
Description: Unexpected error

java.lang.NullPointerException
	at axf.<init>(SourceFile:18)
	at axb.a(SourceFile:62)
	at bho.b(SourceFile:702)
	at awb.V(SourceFile:713)
	at awb.e(SourceFile:642)
	at net.minecraft.client.main.Main.main(SourceFile:103)


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

-- Head --
Stacktrace:
	at axf.<init>(SourceFile:18)
	at axb.a(SourceFile:62)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bfn['Lomny'/42, l='MpServer', x=12,42, y=66,62, z=14,81]]
	Chunk stats: MultiplayerChunkCache: 315, 315
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (11,66,-28), Chunk: (at 11,4,4 in 0,-2; contains blocks 0,0,-32 to 15,255,-17), Region: (0,-1; contains chunks 0,-32 to 31,-1, blocks 0,0,-512 to 511,255,-1)
	Level time: 273670 game time, 273670 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: survival (ID 0). Hardcore: false. Cheats: false
	Forced entities: 40 total; [sf['Pollo'/3, l='MpServer', x=-33,41, y=64,00, z=-0,56], sf['Pollo'/4, l='MpServer', x=-32,69, y=64,00, z=-1,56], sf['Pollo'/6, l='MpServer', x=-23,56, y=64,00, z=26,44], sf['Pollo'/8, l='MpServer', x=-5,63, y=65,00, z=-13,56], sf['Pollo'/10, l='MpServer', x=-13,38, y=65,00, z=1,56], tw['Creeper'/808250, l='MpServer', x=21,50, y=53,00, z=50,50], sn['Maiale'/11, l='MpServer', x=0,69, y=66,00, z=8,56], sf['Pollo'/13, l='MpServer', x=-13,38, y=64,00, z=28,56], sf['Pollo'/14, l='MpServer', x=-15,47, y=64,00, z=20,53], sf['Pollo'/16, l='MpServer', x=-6,44, y=65,00, z=-40,38], sg['Mucca'/19, l='MpServer', x=2,38, y=66,00, z=6,56], sf['Pollo'/18, l='MpServer', x=-7,53, y=64,00, z=31,44], tj['item.item.egg'/757074, l='MpServer', x=-24,16, y=64,13, z=25,53], tj['item.item.egg'/743242, l='MpServer', x=1,81, y=65,13, z=-35,81], sd['Pipistrello'/712657, l='MpServer', x=35,94, y=54,00, z=-1,48], sd['Pipistrello'/736877, l='MpServer', x=38,25, y=55,10, z=0,63], tj['item.item.apple'/773290, l='MpServer', x=32,88, y=79,13, z=21,38], sd['Pipistrello'/698892, l='MpServer', x=36,69, y=55,10, z=0,50], bfn['Lomny'/42, l='MpServer', x=33,66, y=65,62, z=45,70], tj['item.item.egg'/810967, l='MpServer', x=-11,97, y=65,13, z=2,28], sd['Pipistrello'/835894, l='MpServer', x=-10,75, y=17,88, z=50,57], sd['Pipistrello'/813292, l='MpServer', x=17,09, y=49,49, z=49,46], bfn['Lomny'/42, l='MpServer', x=12,42, y=66,62, z=14,81], tj['item.item.egg'/782554, l='MpServer', x=-34,78, y=64,13, z=-1,91], un['Zombi'/835280, l='MpServer', x=-12,50, y=20,00, z=50,50], tj['item.item.egg'/732101, l='MpServer', x=-16,59, y=63,13, z=23,88], sd['Pipistrello'/833120, l='MpServer', x=-9,71, y=16,05, z=49,98], tw['Creeper'/833386, l='MpServer', x=37,50, y=55,00, z=-2,50], bfn['Lomny'/42, l='MpServer', x=30,61, y=85,62, z=19,22], tj['item.item.apple'/827464, l='MpServer', x=31,75, y=86,13, z=18,00], sd['Pipistrello'/627766, l='MpServer', x=35,50, y=55,10, z=4,00], tj['item.tile.sapling.oak'/802959, l='MpServer', x=34,72, y=79,13, z=21,59], tj['item.tile.sapling.oak'/824927, l='MpServer', x=33,84, y=76,13, z=27,44], tj['item.tile.vine'/824926, l='MpServer', x=33,47, y=76,13, z=28,59], tw['Creeper'/834242, l='MpServer', x=-7,50, y=25,00, z=50,50], ui['Scheletro'/716151, l='MpServer', x=39,53, y=54,00, z=0,13], tw['Creeper'/786948, l='MpServer', x=1,50, y=33,00, z=49,50], tj['item.tile.leaves.oak'/729639, l='MpServer', x=30,72, y=83,13, z=19,69], op['Sfera d'Esperienza'/825476, l='MpServer', x=31,06, y=83,23, z=18,63], tj['item.item.egg'/706235, l='MpServer', x=-7,16, y=64,13, z=29,00]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bfi.a(SourceFile:285)
	at awb.b(SourceFile:1813)
	at awb.e(SourceFile:656)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w36b
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
	Memory: 82470104 bytes (78 MB) / 212189184 bytes (202 MB) up to 518979584 bytes (494 MB)
	JVM Flags: 1 total; -Xmx512M
	AABB Pool Size: 4320 (241920 bytes; 0 MB) allocated, 423 (23688 bytes; 0 MB) used
	IntCache: cache: 1, tcache: 1, allocated: 12, tallocated: 94
	Launched Version: 13w36b
	LWJGL: 2.9.0
	OpenGL: GeForce 8500 GT/PCIe/SSE2 GL version 3.3.0, NVIDIA Corporation
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: Italiano (Italia)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1677 (93912 bytes; 0 MB) allocated, 131 (7336 bytes; 0 MB) used