something to do with mob spawners on peaceful

---- Minecraft Crash Report ----
// Ooh. Shiny.

Time: 5/30/13 1:06 PM
Description: Loading entity NBT

java.lang.NullPointerException
	at np.a(SourceFile:357)
	at nq.a(SourceFile:251)
	at sz.a(SourceFile:297)
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhk.a(SourceFile:22)
	at bhk.a(SourceFile:17)
	at bhk.a(SourceFile:12)
	at bhp.a(SourceFile:106)
	at bhp.a(SourceFile:98)
	at bdz.a(SourceFile:317)
	at bds.a(SourceFile:836)
	at bds.b(SourceFile:684)
	at asx.R(SourceFile:674)
	at asx.d(SourceFile:607)
	at net.minecraft.client.main.Main.main(SourceFile:78)


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

-- Head --
Stacktrace:
	at np.a(SourceFile:357)
	at nq.a(SourceFile:251)
	at sz.a(SourceFile:297)

-- Entity being loaded --
Details:
	Entity Type: Skeleton (sz)
	Entity ID: 942
	Entity Name: Skeleton
	Entity's Exact location: 0.00, 0.00, 0.00
	Entity's Block location: World: (0,0,0), Chunk: (at 0,0,0 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)
	Entity's Momentum: 0.00, 0.00, 0.00
Stacktrace:
	at mx.f(SourceFile:1061)
	at aas.a(SourceFile:116)
	at aas.h(SourceFile:234)
	at bhk.a(SourceFile:22)
	at bhk.a(SourceFile:17)
	at bhk.a(SourceFile:12)

-- Tile Entity Details --
Details:
	Name: MobSpawner // arm
	Block type: ID #52 (tile.mobSpawner // aol)
	Block data value: 0 / 0x0 / 0b0000
	Block location: World: (-45,52,89), Chunk: (at 3,3,9 in -3,5; contains blocks -48,0,80 to -33,255,95), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Actual block type: ID #52 (tile.mobSpawner // aol)
	Actual block data value: 0 / 0x0 / 0b0000
Stacktrace:
	at bhp.a(SourceFile:106)
	at bhp.a(SourceFile:98)
	at bdz.a(SourceFile:317)
	at bds.a(SourceFile:836)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bbw['douglasdylan50'/12, l='MpServer', x=-59.32, y=82.04, z=56.03]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (27,135,703), Chunk: (at 11,8,15 in 1,43; contains blocks 16,0,688 to 31,255,703), Region: (0,1; contains chunks 0,32 to 31,63, blocks 0,0,512 to 511,255,1023)
	Level time: 1822110 game time, 624911 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: 26 total; [qw['Bat'/890, l='MpServer', x=-100.63, y=45.99, z=135.82], bbw['douglasdylan50'/12, l='MpServer', x=-59.32, y=82.04, z=56.03], sc['entity.MinecartChest.name'/15, l='MpServer', x=-112.50, y=87.50, z=55.50], qw['Bat'/804, l='MpServer', x=-41.56, y=41.96, z=110.63], sa['item.tile.stoneSlab.sand'/17, l='MpServer', x=-107.88, y=84.13, z=39.13], sg['entity.MinecartRideable.name'/16, l='MpServer', x=-112.22, y=87.50, z=60.50], sg['entity.MinecartRideable.name'/19, l='MpServer', x=-108.72, y=87.50, z=60.50], sg['entity.MinecartRideable.name'/18, l='MpServer', x=-107.50, y=87.50, z=60.50], qw['Bat'/563, l='MpServer', x=-40.47, y=52.88, z=99.57], sg['entity.MinecartRideable.name'/20, l='MpServer', x=-110.47, y=87.50, z=60.50], qw['Bat'/696, l='MpServer', x=-8.75, y=31.77, z=117.66], qw['Bat'/803, l='MpServer', x=-51.19, y=35.46, z=119.34], qw['Bat'/334, l='MpServer', x=-59.54, y=56.51, z=126.71], qw['Bat'/387, l='MpServer', x=-50.35, y=41.71, z=118.32], qw['Bat'/788, l='MpServer', x=-95.28, y=46.03, z=110.16], sg['entity.MinecartRideable.name'/38, l='MpServer', x=-12.50, y=62.50, z=52.41], sj['entity.MinecartTNT.name'/39, l='MpServer', x=-11.53, y=62.50, z=51.50], sg['entity.MinecartRideable.name'/36, l='MpServer', x=-11.41, y=62.50, z=54.50], sg['entity.MinecartRideable.name'/37, l='MpServer', x=-8.50, y=62.50, z=54.50], qw['Bat'/918, l='MpServer', x=-10.64, y=44.35, z=122.95], sg['entity.MinecartRideable.name'/43, l='MpServer', x=5.50, y=63.50, z=11.81], sj['entity.MinecartTNT.name'/40, l='MpServer', x=-10.22, y=62.50, z=54.50], qw['Bat'/497, l='MpServer', x=13.13, y=62.17, z=52.98], qw['Bat'/44, l='MpServer', x=3.63, y=61.10, z=50.13], sg['entity.MinecartRideable.name'/49, l='MpServer', x=22.06, y=63.50, z=2.50], qw['Bat'/896, l='MpServer', x=8.56, y=63.84, z=42.53]]
	Retry entities: 0 total; []
Stacktrace:
	at bbt.a(SourceFile:282)
	at asx.b(SourceFile:1793)
	at asx.d(SourceFile:616)
	at net.minecraft.client.main.Main.main(SourceFile:78)

-- System Details --
Details:
	Minecraft Version: 13w22a
	Operating System: Windows XP (x86) ve