The bug

Most properties in worldgen settings don't have a default which causes the dimension not to load. You get an error like "No key natural in MapLike...". All other data driven files provide these defaults for when you leave out certain options.

How to reproduce

1. Download the worldgen settings no_defaults.json. This is missing the "natural" boolean property.
2. Create a new world and select the downloaded file when importing world settings
   A warning is shown that the "natural" key is missing and the dimension won't exist when you load the world.