Setting level-name to nothing in server.properties causes the server to generate the world files in the server directory.
I would expect an empty level-name to be treated as invalid.
MC-202484
Empty level-name causes server to create world files in server directory
Resolved
Invalid
1
The value in level-name is the directory that the world folder should be in relative to the server folder, so leaving blank would mean putting it in the root directory relative to the server folder, putting it in the server folder. Therefore I think this is invalid