Game crashes when loading worlds

I tried to load a world, but the game crashed.

What I expected to happen was...:
I was expecting the world loading as usual.

What actually happened was...:
When I tried to launch my (singleplayer creative mode vanilla 1.11) world, Minecraft crashes, leaving a report in the launcher

Steps to Reproduce:
1. This may not be true of other users, but just launch a singleplayer world

java.lang.NullPointerException: Exception ticking world
	at ayp.a(SourceFile:41)
	at ayl.a(SourceFile:95)
	at avv.b(SourceFile:437)
	at aum.a(SourceFile:803)
	at aum.a(SourceFile:791)
	at lv.c(SourceFile:115)
	at mb.a(SourceFile:85)
	at mc.c(SourceFile:147)
	at lw.d(SourceFile:221)
	at net.minecraft.server.MinecraftServer.D(SourceFile:626)
	at net.minecraft.server.MinecraftServer.C(SourceFile:562)
	at cce.C(SourceFile:154)
	at net.minecraft.server.MinecraftServer.run(SourceFile:466)
	at java.lang.Thread.run(Thread.java:745)