[MC-129346] Superflat water world (or more but didn't test)

If you want to generate a superflat waterworld it wil just stay at loading world

[0509/210726:INFO:GameCallbacks.cpp(178)] game/net.minecraft.server.MinecraftServer (Server thread) error Encountered an unexpected exception
java.lang.NullPointerException
	at bbr.a(SourceFile:480)
	at bqr.f(SourceFile:85)
	at bqr.<init>(SourceFile:60)
	at bpe$$Lambda$798/767866250.create(Unknown Source)
	at bpe.create(SourceFile:50)
	at bqh.n(SourceFile:81)
	at sj.p(SourceFile:598)
	at sj.<init>(SourceFile:131)
	at dhm.a(SourceFile:97)
	at dhm.d(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:497)
	at java.lang.Thread.run(Thread.java:745)