Unable to export in Lightroom

Lightroom 7.2
Unable to export edited photos:
"Unexpected error performing command: bad argument #1 to 'stringByAppendingPathComponent' (string expected, got nil)"
Exporting pictures were fine an hour before, all of a sudden nothing works. "SHIFT + E" does nothing, the error message above appears only when exporting as JPG (small), JPG (large) & Original + Settings.
I've tried resetting my preferences, reinstalling lightroom, removed similar named files. Please help!
