[MC-124972] Game crashes during the loading world, when creating a superflat world with oceanmonument tag

The bug

Game crashes during the loading world, when creating a superflat world with oceanmonument tag.

minecraft:bedrock,10*minecraft:water;24;oceanmonument

Crash report

18w20c: crash-2018-05-19_12.23.43-server.txt

Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at bbx.a(SourceFile:479)
	at bqx.g(SourceFile:85)
	at bqx.<init>(SourceFile:60)
	at bpk$$Lambda$873/394312725.create(Unknown Source)
	at bpk.create(SourceFile:50)
	at bqn.n(SourceFile:81)
	at sk.p(SourceFile:598)
	at sk.<init>(SourceFile:131)
	at dhr.a(SourceFile:97)
	at dhr.d(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:502)
	at java.lang.Thread.run(Thread.java:745)

18w21a

Description: Exception in server tick loop
java.lang.NullPointerException: Exception in server tick loop
	at bby.a(SourceFile:479)
	at brn.g(SourceFile:85)
	at brn.<init>(SourceFile:60)
	at bqa$$Lambda$917/502381892.create(Unknown Source)
	at bqa.create(SourceFile:50)
	at brd.n(SourceFile:81)
	at sk.p(SourceFile:598)
	at sk.<init>(SourceFile:131)
	at dii.a(SourceFile:97)
	at dii.d(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:502)
	at java.lang.Thread.run(Thread.java:745)

18w22b

Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
	at bca.a(SourceFile:479)
	at brp.g(SourceFile:85)
	at brp.<init>(SourceFile:60)
	at bqc.create(SourceFile:50)
	at brf.n(SourceFile:81)
	at sm.p(SourceFile:598)
	at sm.<init>(SourceFile:131)
	at dik.a(SourceFile:97)
	at dik.d(SourceFile:132)
	at net.minecraft.server.MinecraftServer.run(SourceFile:501)
	at java.lang.Thread.run(Unknown Source)