[MC-187673] [Crash] "java.lang.IllegalStateException: Unregistered dimension type"

The bug

When creating a custom world with the dimension type defined as an object, the game crashes. This essentially means that you cannot define custom dimensions when importing world settings when creating a new world. This crash also happens when loading a dimension inside a data pack that uses an object as dimension type, rather than a string referencing a dimension type.

(1.16 Pre-Release 2) crash-2020-06-05_12.19.07-server.txt

Description: Exception in server tick loop

java.lang.IllegalStateException: Unregistered dimension type: cic@50cbe633
	at net.minecraft.server.MinecraftServer.a(SourceFile:407)
	at net.minecraft.server.MinecraftServer$$Lambda$3891/471301969.get(Unknown Source)
	at java.util.Optional.orElseThrow(Optional.java:290)
	at net.minecraft.server.MinecraftServer.a(SourceFile:407)
	at net.minecraft.server.MinecraftServer.l_(SourceFile:334)
	at eov.d(SourceFile:69)
	at net.minecraft.server.MinecraftServer.v(SourceFile:646)
	at net.minecraft.server.MinecraftServer.a(SourceFile:256)
	at net.minecraft.server.MinecraftServer$$Lambda$3854/1593184149.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:745)

How to reproduce

Download the attached world settings file mc-187673.json
Create a new world and use the import world button
The game crashes