If anyone has not yet migrated their Apple Aperture library to Lightroom or some other ongoing photo processing software, be aware that upgrading your OS to Catalina (10.15) will finally break it completely. You will not be able to open Aperture at all after the update.
AppleInsider claims that it will be much more difficult to migrate after the OS upgrade, so best to do it before. I'm not sure if that's true (the migration tool in LR Classic still seems functional), but it is probably prudent not to tempt fate.