[MC-129383] Loading 18w16a worlds in 18w19b: [WorldGen-Worker-1/ERROR]: Couldn't load chunk

This

[11:04:26] [WorldGen-Worker-1/ERROR]: Couldn't load chunk
java.lang.NullPointerException: null

Millions of times.

When loading a world from 18w16a

Examining the log further...

[11:03:24] [Server thread/ERROR]: Couldn't load chunk
java.lang.NullPointerException: null
	at bqt.<init>(SourceFile:70) ~[minecraft_server.18w19b.jar:?]
	at bpl.c(SourceFile:627) ~[minecraft_server.18w19b.jar:?]
	at java.util.HashMap.computeIfAbsent(Unknown Source) ~[?:1.8.0_171]
	at bpl.a(SourceFile:627) ~[minecraft_server.18w19b.jar:?]
	at bpx.a(SourceFile:455) ~[minecraft_server.18w19b.jar:?]
	at bpx.a(SourceFile:150) ~[minecraft_server.18w19b.jar:?]
	at bpx.a(SourceFile:98) ~[minecraft_server.18w19b.jar:?]
	at si.g(SourceFile:94) [minecraft_server.18w19b.jar:?]
	at si.b(SourceFile:118) [minecraft_server.18w19b.jar:?]
	at si.a(SourceFile:160) [minecraft_server.18w19b.jar:?]
	at net.minecraft.server.MinecraftServer.g_(SourceFile:384) [minecraft_server.18w19b.jar:?]
	at net.minecraft.server.MinecraftServer.a(SourceFile:336) [minecraft_server.18w19b.jar:?]
	at ru.d(SourceFile:247) [minecraft_server.18w19b.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:497) [minecraft_server.18w19b.jar:?]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_171]