https://pastebin.com/zRGsiWZY
Get stuck on "Loading World", going into folder there's this crash, when creating New World, type Superflat, preset Void

I can generate Space though

at mcjty.lostcities.dimensions.world.WorldTypeTools.getProfileOnServer(WorldTypeTools.java:77)
at mcjty.lostcities.dimensions.world.WorldTypeTools.getProfile(WorldTypeTools.java:34)
at mcjty.lostcities.ForgeEventHandlers.onCreateSpawnPoint(ForgeEventHandlers.java:39)

It looks like the problem is that at no point in those three methods do we ever check whether the world being generated is a Lost Cities world, but then we try to parse world.getWorldInfo().getGeneratorOptions() as if it were JSON, which it isn't if this isn't a Lost Cities world (instead it's something like 3;minecraft:air;127;decoration).

Fixed next release