It looks like the issue is caused by Java 9... according to the log, certain methods of the underlying engine are not supported anymore by Java 9.
Actually the game and the server haven't been tested with Java 9 yet. I'd recommend to rollback to Java 8 (unless you run software which requires at least Java 9, there should be nothing to worry about by using Java and see if the issue still persists
It's the right solution, it works now. Thank you.