After having set level-type to flat and generator-settings to a seemingly correct superflat preset, starting the server did not work. It didn't crash, it never started at all. The log is attached along with the server.properties file of the server.
What I expected to happen was:
The server would throw an error, ignore the generator-settings property and then start correctly.
What actually happened was:
The server did not start.
This is actually a duplicate of MC-186153.