summon bug

i was did /summon Fireball ~ ~3 ~

this is my error:

---- Minecraft Crash Report ----
// I'm sorry, Dave.

Time: 10/10/13 7:08 PM
Description: Unexpected error

java.lang.NullPointerException
	at bkv.a(SourceFile:303)
	at bkv.a(SourceFile:900)
	at bkv.b(SourceFile:816)
	at ays.ab(SourceFile:783)
	at ays.e(SourceFile:706)
	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 bkv.a(SourceFile:303)
	at bkv.a(SourceFile:900)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bip['XxJoshCraftxX'/79, l='MpServer', x=367.78, y=64.62, z=83.18]]
	Chunk stats: MultiplayerChunkCache: 255, 255
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (124,64,256), Chunk: (at 12,4,0 in 7,16; contains blocks 112,0,256 to 127,255,271), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 9268 game time, 9268 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: 74 total; [uy['Squid'/136, l='MpServer', x=400.06, y=59.34, z=73.50], wr['Skeleton'/141, l='MpServer', x=389.50, y=23.00, z=96.50], wf['Creeper'/2608, l='MpServer', x=330.50, y=41.00, z=147.50], ww['Zombie'/142, l='MpServer', x=392.22, y=18.00, z=103.50], uy['Squid'/131, l='MpServer', x=394.91, y=56.31, z=60.84], uy['Squid'/130, l='MpServer', x=402.34, y=56.72, z=78.66], uy['Squid'/132, l='MpServer', x=386.50, y=54.13, z=55.31], uk['Bat'/134, l='MpServer', x=398.28, y=25.35, z=90.53], wr['Skeleton'/152, l='MpServer', x=408.41, y=27.00, z=124.91], ww['Zombie'/153, l='MpServer', x=410.50, y=18.00, z=127.50], uk['Bat'/4151, l='MpServer', x=305.75, y=18.10, z=8.75], wf['Creeper'/157, l='MpServer', x=408.50, y=45.00, z=160.50], wf['Creeper'/2592, l='MpServer', x=325.50, y=31.00, z=52.50], vs['entity.MinecartChest.name'/158, l='MpServer', x=429.50, y=34.50, z=33.50], wr['Skeleton'/159, l='MpServer', x=429.50, y=52.00, z=74.50], wf['Creeper'/144, l='MpServer', x=411.50, y=36.00, z=69.50], uk['Bat'/4274, l='MpServer', x=322.78, y=32.24, z=101.09], wf['Creeper'/2607, l='MpServer', x=331.50, y=41.00, z=145.50], wf['Creeper'/4397, l='MpServer', x=295.50, y=36.00, z=149.00], wr['Skeleton'/2603, l='MpServer', x=314.50, y=18.00, z=10.50], ww['Zombie'/150, l='MpServer', x=407.34, y=16.00, z=114.34], uy['Squid'/163, l='MpServer', x=420.69, y=61.09, z=90.03], uy['Squid'/161, l='MpServer', x=424.50, y=60.28, z=91.47], wg['Enderman'/160, l='MpServer', x=424.34, y=44.00, z=83.41], wt['Spider'/3669, l='MpServer', x=350.88, y=33.00, z=145.63], uy['Squid'/164, l='MpServer', x=413.53, y=59.38, z=93.50], ww['Zombie'/186, l='MpServer', x=440.50, y=29.00, z=142.25], wf['Creeper'/1870, l='MpServer', x=339.50, y=19.00, z=25.50], ww['Zombie'/188, l='MpServer', x=439.50, y=35.00, z=134.50], um['Chicken'/189, l='MpServer', x=438.44, y=103.00, z=153.59], ww['Zombie'/176, l='MpServer', x=433.50, y=43.00, z=78.50], wf['Creeper'/177, l='MpServer', x=437.50, y=43.00, z=79.50], wf['Creeper'/181, l='MpServer', x=437.00, y=46.00, z=84.59], uu['Pig'/77, l='MpServer', x=317.53, y=73.00, z=69.31], uu['Pig'/78, l='MpServer', x=304.59, y=65.00, z=81.50], uu['Pig'/74, l='MpServer', x=301.50, y=66.00, z=79.50], uu['Pig'/75, l='MpServer', x=302.56, y=68.00, z=81.75], bip['XxJoshCraftxX'/79, l='MpServer', x=367.78, y=64.62, z=83.18], uk['Bat'/80, l='MpServer', x=386.75, y=26.10, z=93.25], ww['Zombie'/2937, l='MpServer', x=289.50, y=39.00, z=145.50], wr['Skeleton'/94, l='MpServer', x=342.75, y=61.01, z=124.25], uu['Pig'/89, l='MpServer', x=320.50, y=75.00, z=147.84], wf['Creeper'/2940, l='MpServer', x=290.75, y=37.00, z=150.06], uu['Pig'/88, l='MpServer', x=322.22, y=78.00, z=154.78], uu['Pig'/91, l='MpServer', x=322.19, y=77.00, z=151.16], uu['Pig'/90, l='MpServer', x=323.81, y=78.00, z=153.47], uk['Bat'/1942, l='MpServer', x=356.45, y=11.00, z=142.42], uk['Bat'/1943, l='MpServer', x=361.75, y=14.34, z=135.50], wf['Creeper'/3249, l='MpServer', x=341.50, y=35.00, z=3.50], uk['Bat'/1941, l='MpServer', x=371.44, y=13.90, z=141.72], uk['Bat'/1939, l='MpServer', x=376.48, y=15.68, z=134.94], wr['Skeleton'/5119, l='MpServer', x=351.50, y=29.00, z=110.50], wr['Skeleton'/5120, l='MpServer', x=354.38, y=25.00, z=101.88], uk['Bat'/5104, l='MpServer', x=333.04, y=36.65, z=139.08], wr['Skeleton'/111, l='MpServer', x=359.03, y=32.00, z=139.88], uk['Bat'/5106, l='MpServer', x=386.56, y=27.43, z=105.31], ww['Zombie'/109, l='MpServer', x=354.50, y=29.00, z=107.50], wf['Creeper'/5125, l='MpServer', x=440.50, y=45.00, z=70.00], wr['Skeleton'/5124, l='MpServer', x=431.50, y=38.00, z=125.50], xm['Fireball'/5695, l='MpServer', x=367.50, y=66.00, z=83.50], wg['Enderman'/115, l='MpServer', x=360.69, y=33.00, z=135.75], wf['Creeper'/5150, l='MpServer', x=323.50, y=18.00, z=20.50], wf['Creeper'/2144, l='MpServer', x=347.50, y=28.00, z=125.50], wf['Creeper'/2631, l='MpServer', x=343.50, y=15.00, z=113.50], wr['Skeleton'/112, l='MpServer', x=358.66, y=32.00, z=135.97], wr['Skeleton'/2632, l='MpServer', x=346.50, y=35.00, z=131.50], ww['Zombie'/601, l='MpServer', x=383.50, y=25.00, z=84.50], wr['Skeleton'/5515, l='MpServer', x=343.50, y=31.00, z=153.50], wr['Skeleton'/2633, l='MpServer', x=348.50, y=35.00, z=131.50], ww['Zombie'/600, l='MpServer', x=386.50, y=25.00, z=85.50], uk['Bat'/125, l='MpServer', x=388.47, y=26.79, z=81.75], ww['Zombie'/5140, l='MpServer', x=296.50, y=23.00, z=26.50], wf['Creeper'/2636, l='MpServer', x=347.50, y=35.00, z=131.50], wr['Skeleton'/604, l='MpServer', x=363.09, y=13.00, z=134.50]]
	Retry entities: 0 total; []
	Server brand: vanilla
	Server type: Integrated singleplayer server
Stacktrace:
	at bik.a(SourceFile:302)
	at ays.b(SourceFile:1924)
	at ays.e(SourceFile:720)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w41a
	Operating System: Mac OS X (x86_64) version 10.8.5
	Java Version: 1.6.0_51, Apple Inc.
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
	Memory: 85674376 bytes (81 MB) / 229564416 bytes (218 MB) up to 1065025536 bytes (1015 MB)
	JVM Flags: 1 total; -Xmx1g
	AABB Pool Size: 2644 (148064 bytes; 0 MB) allocated, 2587 (144872 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Launched Version: 13w41a
	LWJGL: 2.9.0
	OpenGL: Intel HD Graphics 3000 OpenGL Engine GL version 2.1 INTEL-8.16.74, Intel Inc.
	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)
	Vec3 Pool Size: 1818 (101808 bytes; 0 MB) allocated, 664 (37184 bytes; 0 MB) used