Crash when saving and returning to the title screen

The bug

Whenever you're in a single player world, trying to click "Save and Quit to Title" in the Game Menu will crash the game.

Crash report

---- Minecraft Crash Report ----
// This is a token for 1 free hug. Redeem at your nearest Mojangsta: [~~HUG~~]

Time: 4/20/17 6:28 PM
Description: Unexpected error

java.lang.NullPointerException: Unexpected error
	at cgr.a(SourceFile:59)
	at cgv.a(SourceFile:41)
	at bgy.t(SourceFile:1554)
	at bgy.ax(SourceFile:964)
	at bgy.a(SourceFile:404)
	at net.minecraft.client.main.Main.main(SourceFile:123)


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

-- System Details --
Details:
	Minecraft Version: 17w16a
	Operating System: Windows 10 (amd64) version 10.0
	Java Version: 1.8.0_51, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 260660936 bytes (248 MB) / 366252032 bytes (349 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: 1, tcache: 1, allocated: 12, tallocated: 94
	Launched Version: 17w16a
	LWJGL: 2.9.4
	OpenGL: GeForce GTX 860M/PCIe/SSE2 GL version 4.5.0 NVIDIA 381.65, 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: Yes
	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: 8x Intel(R) Core(TM) i7-4720HQ CPU @ 2.60GHz

Hopper

MCX-3502952