what the?

i was testing the wings, and i suddenly tossed to somewhere, there was a invisible mountain, i just be like wtf and reopened the save but minecraft is crashed.

This is appeared in the crash log:

-- Head --
Stacktrace:
	at ahc.a(SourceFile:1118)
	at bku.h(SourceFile:1602)
	at bku.a(SourceFile:1178)
	at bku.b(SourceFile:1163)

-- Affected level --
Details:
	Level name: MpServer
	All players: 0 total; []
	Chunk stats: MultiplayerChunkCache: 0, 0
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (8,64,8), Chunk: (at 8,4,8 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)
	Level time: 0 game time, 0 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: 0 total; []
	Retry entities: 0 total; []
	Server brand: ~~ERROR~~ NullPointerException: null
	Server type: Integrated singleplayer server
Stacktrace:
	at bii.a(SourceFile:362)
	at bab.b(SourceFile:2389)
	at bab.a(SourceFile:393)
	at net.minecraft.client.main.Main.main(SourceFile:125)

-- System Details --
Details:
	Minecraft Version: 15w41b
	Operating System: Windows 10 (x86) version 10.0
	Java Version: 1.8.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 384667000 bytes (366 MB) / 610955264 bytes (582 MB) up to 1046937600 bytes (998 MB)
	JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn256M
	IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
	Launched Version: 15w41b
	LWJGL: 2.9.4
	OpenGL: GeForce 9800 GT/PCIe/SSE2/3DNOW! GL version 3.3.0, NVIDIA Corporation
	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 AMD Athlon(tm) II X4 645 Processor