Just upgraded from 8.3 to 8.5 with the full ModelsBuilder installed. I now can't create or update document types.
I get the following error:

I also tried to install an empty 8.5 from nuget. When full ModelsBuilder is installed, the same error is shown.
If I uninstall ModelsBuilder creating and saving document types works again.
馃槺
We're working on it!
Thanks for the report, can reproduce unfortunately, working on a PR now. Sorry about this, we did test this scenario of course, I'm not sure what went wrong during testing! 馃槹
No worries, just glad you are working on a quick fix 馃槃