I was in survival, and I found an iron helmet in a dungeon. When I right-clicked to put the armor on, the game crashed. Upon reloading the world, the armor was removed from my inventory (no I was not wearing it). I created a new world with cheats enabled, and used the console to get a (different) piece of armor. When I right clicked, once again, the game crashed.

---- Minecraft Crash Report ----
// Everything's going to plan. No, really, that was supposed to happen.

Time: 12/4/15 9:13 PM
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
at rx.a_(SourceFile:409)
at zo.a(SourceFile:1818)
at rx.a(SourceFile:1198)
at bkg.a(SourceFile:373)
at bbz.au(SourceFile:1450)
at bbz.ax(SourceFile:1934)
at bbz.aw(SourceFile:1752)
at bbz.s(SourceFile:1596)
at bbz.as(SourceFile:942)
at bbz.a(SourceFile:386)
at net.minecraft.client.main.Main.main(SourceFile:122)

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

– Head –
Stacktrace:
at rx.a_(SourceFile:409)
at zo.a(SourceFile:1818)
at rx.a(SourceFile:1198)
at bkg.a(SourceFile:373)
at bbz.au(SourceFile:1450)
at bbz.ax(SourceFile:1934)
at bbz.aw(SourceFile:1752)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bmg['Mr_Regrub6'/323, l='MpServer', x=-44.03, y=64.00, z=267.50]]
Chunk stats: MultiplayerChunkCache: 361, 361
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (-52,64,252), Chunk: (at 12,4,12 in -4,15; contains blocks -64,0,240 to -49,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 1213 game time, 1213 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: 63 total; [wa['Sheep'/256, l='MpServer', x=-24.53, y=62.44, z=276.16], yb['container.minecart'/259, l='MpServer', x=-14.50, y=30.06, z=198.50], bmg['Mr_Regrub6'/323, l='MpServer', x=-44.03, y=64.00, z=267.50], yb['container.minecart'/260, l='MpServer', x=-5.50, y=33.06, z=192.50], xz['item.tile.torch'/261, l='MpServer', x=-2.53, y=35.00, z=228.19], wa['Sheep'/262, l='MpServer', x=-12.88, y=68.00, z=244.06], wa['Sheep'/263, l='MpServer', x=-7.91, y=68.00, z=247.84], vq['Bat'/264, l='MpServer', x=1.05, y=12.00, z=265.11], wa['Sheep'/136, l='MpServer', x=-99.50, y=66.00, z=210.50], wa['Sheep'/137, l='MpServer', x=-102.50, y=67.00, z=221.69], vq['Bat'/265, l='MpServer', x=-2.45, y=11.95, z=342.71], wa['Sheep'/138, l='MpServer', x=-94.34, y=67.00, z=219.44], wa['Sheep'/139, l='MpServer', x=-98.50, y=66.00, z=210.50], vt['Chicken'/140, l='MpServer', x=-100.56, y=73.00, z=269.34], vt['Chicken'/141, l='MpServer', x=-100.50, y=73.00, z=268.50], vt['Chicken'/142, l='MpServer', x=-102.56, y=76.00, z=278.34], vt['Chicken'/143, l='MpServer', x=-98.50, y=75.00, z=274.34], wa['Sheep'/150, l='MpServer', x=-90.50, y=75.00, z=275.50], vq['Bat'/1942, l='MpServer', x=-94.53, y=38.69, z=310.66], wa['Sheep'/151, l='MpServer', x=-92.50, y=75.00, z=274.50], wa['Sheep'/152, l='MpServer', x=-95.50, y=76.00, z=276.50], wa['Sheep'/153, l='MpServer', x=-102.78, y=73.00, z=269.59], wa['Sheep'/188, l='MpServer', x=-68.50, y=68.00, z=228.50], wa['Sheep'/189, l='MpServer', x=-70.94, y=68.00, z=225.88], wa['Sheep'/190, l='MpServer', x=-69.44, y=68.00, z=225.19], vq['Bat'/191, l='MpServer', x=-56.55, y=26.93, z=319.69], vq['Bat'/192, l='MpServer', x=-74.24, y=32.38, z=320.26], wa['Sheep'/208, l='MpServer', x=-48.63, y=68.00, z=200.53], wa['Sheep'/209, l='MpServer', x=-49.72, y=67.00, z=200.50], wa['Sheep'/210, l='MpServer', x=-51.50, y=66.00, z=200.50], wa['Sheep'/211, l='MpServer', x=-61.28, y=66.00, z=218.53], wa['Sheep'/212, l='MpServer', x=-52.38, y=66.00, z=207.16], vu['Cow'/213, l='MpServer', x=-48.81, y=56.00, z=300.50], wa['Sheep'/214, l='MpServer', x=-51.09, y=63.00, z=298.00], vq['Bat'/215, l='MpServer', x=-59.72, y=27.25, z=303.53], vq['Bat'/216, l='MpServer', x=-54.69, y=30.10, z=324.25], wa['Sheep'/217, l='MpServer', x=-48.50, y=63.00, z=327.50], vq['Bat'/95, l='MpServer', x=-126.01, y=14.27, z=300.23], wa['Sheep'/227, l='MpServer', x=-47.56, y=69.00, z=197.31], wa['Sheep'/228, l='MpServer', x=-33.47, y=65.00, z=222.22], vq['Bat'/229, l='MpServer', x=-39.65, y=30.29, z=234.75], wa['Sheep'/230, l='MpServer', x=-38.50, y=64.00, z=224.44], wa['Sheep'/231, l='MpServer', x=-36.94, y=65.00, z=226.16], wa['Sheep'/232, l='MpServer', x=-35.31, y=63.00, z=268.50], vu['Cow'/233, l='MpServer', x=-51.60, y=65.41, z=271.44], wa['Sheep'/234, l='MpServer', x=-38.91, y=62.00, z=269.94], wa['Sheep'/235, l='MpServer', x=-51.92, y=60.00, z=272.27], wa['Sheep'/236, l='MpServer', x=-44.50, y=64.00, z=282.50], wa['Sheep'/237, l='MpServer', x=-36.00, y=63.00, z=276.97], wa['Sheep'/238, l='MpServer', x=-43.00, y=64.00, z=285.97], vu['Cow'/239, l='MpServer', x=-34.56, y=63.00, z=301.41], vu['Cow'/240, l='MpServer', x=-32.31, y=63.00, z=298.25], vu['Cow'/241, l='MpServer', x=-33.06, y=63.00, z=299.19], wa['Sheep'/242, l='MpServer', x=-32.53, y=63.00, z=302.78], wa['Sheep'/243, l='MpServer', x=-39.28, y=63.00, z=298.53], wa['Sheep'/244, l='MpServer', x=-47.74, y=64.00, z=286.97], wa['Sheep'/245, l='MpServer', x=-36.97, y=63.00, z=292.16], xz['item.item.arrow'/246, l='MpServer', x=-36.13, y=56.00, z=315.88], xz['item.item.bone'/247, l='MpServer', x=-36.88, y=56.00, z=315.88], wa['Sheep'/248, l='MpServer', x=-44.50, y=63.00, z=325.50], wa['Sheep'/249, l='MpServer', x=-46.50, y=62.13, z=320.63], wa['Sheep'/254, l='MpServer', x=-23.84, y=64.00, z=254.53], wa['Sheep'/255, l='MpServer', x=-18.50, y=68.00, z=250.31]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bkh.a(SourceFile:364)
at bbz.b(SourceFile:2496)
at bbz.a(SourceFile:400)
at net.minecraft.client.main.Main.main(SourceFile:122)

– System Details –
Details:
Minecraft Version: 15w49a
Operating System: Mac OS X (x86_64) version 10.11.1
Java Version: 1.8.0_60, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 279943840 bytes (266 MB) / 439975936 bytes (419 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 5 total; -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: 15w49a
LWJGL: 2.9.2
OpenGL: ATI Radeon HD 4670 OpenGL Engine GL version 2.1 ATI-10.0.40, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because ARB_framebuffer_object 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) i3 CPU 540 @ 3.07GHz