Floating Island generated world instantly crashes on joining

When loading a buffet world with floating island generator setting it loads the world but then instantly crashes when my player joins the world. I have tried using all pre-release versions prior to 1.13pre-9 which do not throw the same crash when loading or creating a buffet floating island world save.

What should happen:
The world generates itself and world spawn is prepared.
The player would then join the world and chunks generate around them on spawning in.

What actually happened:
Spawn chunks were prepared as normal but as soon as my player joins the world, server crashes with an Exception Ticking World error.

Steps to reproduce this:

1. Create a world save in Singleplayer mode.
2. Select buffet world gen setting and select customize
3. Set world generator to "Floating Island" and pick any biome.
4. Hit Create World and wait for it to generate.

I have attached the crash reports from when loading the world save threw the exception.