Hopper: java.lang.IllegalArgumentException: Modifier name cannot be empty

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-83827/

Crash:

java.lang.IllegalArgumentException: Modifier name cannot be empty
	at org.apache.commons.lang3.Validate.notEmpty(Validate.java:398)
	at pi.<init>(SourceFile:31)
	at ug.a(SourceFile:92)
	at yx.D(SourceFile:581)
	at yx.a(SourceFile:471)
	at azw.a(SourceFile:188)
	at bak.a(SourceFile:581)
	at azw.a(SourceFile:168)
	at ban.a(SourceFile:30)
	at bak.a(SourceFile:530)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// You're mean.

Time: 06/09/13 15:34
Description: Rendering screen

java.lang.IllegalArgumentException: Modifier name cannot be empty
	at org.apache.commons.lang3.Validate.notEmpty(Validate.java:398)
	at pi.<init>(SourceFile:31)
	at ug.a(SourceFile:92)
	at yx.D(SourceFile:581)
	at yx.a(SourceFile:471)
	at azw.a(SourceFile:188)
	at bak.a(SourceFile:581)
	at azw.a(SourceFile:168)
	at ban.a(SourceFile:30)
	at bak.a(SourceFile:530)
	at bho.b(SourceFile:720)
	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 org.apache.commons.lang3.Validate.notEmpty(Validate.java:398)
	at pi.<init>(SourceFile:31)
	at ug.a(SourceFile:92)
	at yx.D(SourceFile:581)
	at yx.a(SourceFile:471)
	at azw.a(SourceFile:188)
	at bak.a(SourceFile:581)
	at azw.a(SourceFile:168)
	at ban.a(SourceFile:30)
	at bak.a(SourceFile:530)

-- Screen render details --
Details:
	Screen name: bak
	Mouse location: Scaled: (288, 200). Absolute: (866, 237)
	Screen size: Scaled: (480, 280). Absolute: (1440, 838). Scale factor of 3

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bfn['Olivman7'/42, l='MpServer', x=-685,79, y=57,62, z=509,97]]
	Chunk stats: MultiplayerChunkCache: 270, 270
	Level seed: 0
	Level generator: ID 01 - flat, ver 0. Features enabled: false
	Level generator options: 
	Level spawn location: World: (-739,4,582), Chunk: (at 13,0,6 in -47,36; contains blocks -752,0,576 to -737,255,591), Region: (-2,1; contains chunks -64,32 to -33,63, blocks -1024,0,512 to -513,255,1023)
	Level time: 3541156 game time, 1000 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: 38 total; [os['entity.ItemFrame.name'/291322, l='MpServer', x=-684,06, y=57,50, z=510,50], os['entity.ItemFrame.name'/8, l='MpServer', x=-752,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/9, l='MpServer', x=-752,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/10, l='MpServer', x=-752,50, y=58,50, z=547,94], tq['entity.MinecartSpawner.name'/11, l='MpServer', x=-760,50, y=61,34, z=574,50], os['entity.ItemFrame.name'/12, l='MpServer', x=-753,50, y=56,50, z=603,06], us['Villager'/13, l='MpServer', x=-736,50, y=56,00, z=538,50], os['entity.ItemFrame.name'/14, l='MpServer', x=-746,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/15, l='MpServer', x=-746,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/17, l='MpServer', x=-749,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/16, l='MpServer', x=-747,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/19, l='MpServer', x=-751,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/18, l='MpServer', x=-750,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/21, l='MpServer', x=-746,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/20, l='MpServer', x=-751,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/23, l='MpServer', x=-748,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/22, l='MpServer', x=-747,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/25, l='MpServer', x=-751,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/24, l='MpServer', x=-749,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/27, l='MpServer', x=-748,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/26, l='MpServer', x=-750,50, y=58,50, z=547,94], os['entity.ItemFrame.name'/29, l='MpServer', x=-751,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/28, l='MpServer', x=-750,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/31, l='MpServer', x=-748,50, y=56,50, z=547,94], os['entity.ItemFrame.name'/30, l='MpServer', x=-749,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/34, l='MpServer', x=-730,50, y=57,50, z=564,06], os['entity.ItemFrame.name'/35, l='MpServer', x=-731,50, y=57,50, z=564,06], os['entity.ItemFrame.name'/32, l='MpServer', x=-747,50, y=57,50, z=547,94], os['entity.ItemFrame.name'/33, l='MpServer', x=-733,50, y=57,50, z=564,06], tp['entity.MinecartRideable.name'/38, l='MpServer', x=-711,50, y=56,50, z=572,22], os['entity.ItemFrame.name'/39, l='MpServer', x=-703,50, y=58,50, z=529,06], os['entity.ItemFrame.name'/36, l='MpServer', x=-732,50, y=57,50, z=564,06], os['entity.ItemFrame.name'/65724, l='MpServer', x=-684,06, y=57,50, z=508,50], os['entity.ItemFrame.name'/37, l='MpServer', x=-734,50, y=57,50, z=564,06], os['entity.ItemFrame.name'/40, l='MpServer', x=-701,50, y=58,50, z=529,06], bfn['Olivman7'/42, l='MpServer', x=-685,79, y=57,62, z=509,97], os['entity.ItemFrame.name'/56787, l='MpServer', x=-684,06, y=57,50, z=506,50], os['entity.ItemFrame.name'/305253, l='MpServer', x=-684,06, y=57,50, z=512,50]]
	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:651)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 13w36b
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 39100472 bytes (37 MB) / 471465984 bytes (449 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 118 (6608 bytes; 0 MB) allocated, 5 (280 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 13w36b
	LWJGL: 2.9.0
	OpenGL: AMD Radeon HD 6570   GL version 4.1.10765 Compatibility Profile Context, ATI Technologies 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: 119 (6664 bytes; 0 MB) allocated, 46 (2576 bytes; 0 MB) used

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-83827/8326585/