[MC-127096] Creating a Water World preset Superflat world crashes the game

Creating a superflat world with preset "Water World" in snapshot 18w10d causes the game to freeze/crash. Only occurs with "Water World" preset: other presets work fine.

Crash Report:

Time: 3/10/18 5:38 PM
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at auw.a(SourceFile:429)
	at bjg.e(SourceFile:60)
	at bjg.<init>(SourceFile:46)
	at biw.o(SourceFile:46)
	at se.o(SourceFile:719)
	at se.<init>(SourceFile:127)
	at cyv.a(SourceFile:96)
	at cyv.d(SourceFile:131)
	at net.minecraft.server.MinecraftServer.run(SourceFile:502)
	at java.lang.Thread.run(Thread.java:745)