I was working on a redstone creation that uses silverfish with custom names. Just to test it, I spawned in a silverfish with a custom name. I killed the silverfish in creative mode with a diamond sword and my game crashed. I did it again just to make sure that the silverfish crashed my game and it my game crashed again.

---- Minecraft Crash Report ----
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Time: 8/28/15 12:18 PM
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
at yf.a(SourceFile:93)
at yt.f(SourceFile:1043)
at bhm.a(SourceFile:366)
at azh.aw(SourceFile:1355)
at azh.s(SourceFile:1856)
at azh.av(SourceFile:926)
at azh.a(SourceFile:375)
at net.minecraft.client.main.Main.main(SourceFile:125)

A detailed walkthrough of the error, its code path and all known details is as follows:
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– Head –
Stacktrace:
at yf.a(SourceFile:93)
at yt.f(SourceFile:1043)
at bhm.a(SourceFile:366)
at azh.aw(SourceFile:1355)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bjm['machinespray'/27, l='MpServer', x=-551.37, y=4.25, z=741.29]]
Chunk stats: MultiplayerChunkCache: 289, 289
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: -538.00,4.00,743.00 - World: (-538,4,743), Chunk: (at 6,0,7 in -34,46; contains blocks -544,0,736 to -529,255,751), Region: (-2,1; contains chunks -64,32 to -33,63, blocks -1024,0,512 to -513,255,1023)
Level time: 714 game time, 714 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: 42 total; [yh['Slime'/1, l='MpServer', x=-617.25, y=4.00, z=685.03], yh['Slime'/2, l='MpServer', x=-588.22, y=4.00, z=716.44], vj['Rabbit'/8706, l='MpServer', x=-593.50, y=4.00, z=711.50], vj['Rabbit'/8707, l='MpServer', x=-591.56, y=4.00, z=700.63], yh['Slime'/28803, l='MpServer', x=-576.72, y=4.00, z=804.47], vj['Rabbit'/8708, l='MpServer', x=-593.72, y=4.00, z=706.25], yh['Slime'/99333, l='MpServer', x=-560.66, y=4.40, z=668.78], vj['Rabbit'/8709, l='MpServer', x=-597.66, y=4.00, z=707.34], yh['Slime'/8, l='MpServer', x=-573.98, y=4.27, z=737.70], yh['Slime'/9, l='MpServer', x=-588.19, y=4.00, z=742.16], yh['Slime'/10, l='MpServer', x=-595.25, y=4.00, z=746.63], yh['Slime'/52234, l='MpServer', x=-573.99, y=4.14, z=748.63], yh['Slime'/12875, l='MpServer', x=-491.71, y=4.91, z=680.65], yh['Slime'/74314, l='MpServer', x=-481.25, y=4.00, z=677.69], yh['Slime'/95754, l='MpServer', x=-489.13, y=4.00, z=679.22], yh['Slime'/12, l='MpServer', x=-561.53, y=4.00, z=805.53], yh['Slime'/13, l='MpServer', x=-554.16, y=4.00, z=678.38], yh['Slime'/15, l='MpServer', x=-522.34, y=4.00, z=812.63], yh['Slime'/16, l='MpServer', x=-511.34, y=4.00, z=705.75], yh['Slime'/17, l='MpServer', x=-506.59, y=4.00, z=689.69], yh['Slime'/81744, l='MpServer', x=-490.91, y=4.00, z=791.59], yh['Slime'/18, l='MpServer', x=-502.91, y=4.00, z=685.03], vi['Pig'/8722, l='MpServer', x=-554.44, y=4.00, z=797.38], vi['Pig'/8723, l='MpServer', x=-552.19, y=4.00, z=798.97], yf['hi'/89106, l='MpServer', x=-554.97, y=4.00, z=741.97], vi['Pig'/8724, l='MpServer', x=-558.06, y=4.00, z=790.94], yh['Slime'/21, l='MpServer', x=-486.84, y=5.22, z=696.59], vi['Pig'/8725, l='MpServer', x=-556.50, y=4.00, z=796.50], yh['Slime'/22934, l='MpServer', x=-504.57, y=4.00, z=686.86], yh['Slime'/12442, l='MpServer', x=-613.38, y=4.00, z=679.38], yh['Slime'/66971, l='MpServer', x=-516.04, y=4.52, z=820.48], bjm['machinespray'/27, l='MpServer', x=-551.37, y=4.25, z=741.29], yh['Slime'/95709, l='MpServer', x=-571.91, y=4.00, z=807.31], yh['Slime'/48797, l='MpServer', x=-495.81, y=5.07, z=696.57], vk['Sheep'/8735, l='MpServer', x=-520.81, y=4.00, z=678.19], vk['Sheep'/8736, l='MpServer', x=-527.81, y=4.00, z=684.31], vk['Sheep'/8737, l='MpServer', x=-523.72, y=4.00, z=681.22], vk['Sheep'/8738, l='MpServer', x=-525.84, y=4.00, z=682.28], yh['Slime'/26092, l='MpServer', x=-568.09, y=4.00, z=808.44], yh['Slime'/33137, l='MpServer', x=-611.06, y=5.00, z=679.75], yh['Slime'/90110, l='MpServer', x=-591.53, y=5.22, z=738.53], yh['Slime'/109950, l='MpServer', x=-564.50, y=4.91, z=803.88]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bhn.a(SourceFile:361)
at azh.b(SourceFile:2361)
at azh.a(SourceFile:389)
at net.minecraft.client.main.Main.main(SourceFile:125)

– System Details –
Details:
Minecraft Version: 15w35c
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 128887480 bytes (122 MB) / 279941120 bytes (266 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 15w35c
LWJGL: 2.9.4
OpenGL: Intel(R) HD Graphics 4400 GL version 4.3.0 - Build 10.18.15.4256, Intel
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
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)
CPU: 4x Intel(R) Core(TM) i5-4300U CPU @ 1.90GHz