Found this link. It is a little old.
http://aurora2.pentarch.org/index.php?topic=2122.0Have you got any officers with apostrophes in their name?
Do you have any officer ranks with an empty name?
Or this reddit thread suggests it could be an issue with one of your Task Groups.
https://www.reddit.com/r/aurora/comments/3z9u4k/error_94_error_in_invalid_use_of_null_and_error/Another reddit thread suggests it could be due to a ship class name that is too long
https://www.reddit.com/r/aurora/comments/7119ot/error_94381_blank_ship_class_design/