Note: This happened to me five times

What I expected to happen was...:
World creation to happen as per normal

What actually happened was...:
Upon creating the world my Minecraft crashed

Steps to Reproduce:

(Creation)
1. Click Singleplayer
2. Click Create New World
3. Change the gamemode to Creative
4. Change the world to Superflat
5. Click Create New World

(Opening)
1. Click Singleplayer
2. Open an already created Superflat world

java.lang.NullPointerException: Unexpected error
	at agv.a(SourceFile:1120)
	at bkt.h(SourceFile:1598)
	at bkt.a(SourceFile:1178)
	at bkt.b(SourceFile:1163)
	at bkt.a(SourceFile:1010)
	at bab.as(SourceFile:954)
	at bab.a(SourceFile:377)
	at net.minecraft.client.main.Main.main(SourceFile:125)