FYI & FWIW
The message "WARNING: Empty NZB file" can mean empty NZB file, but also incorrect or no NZB file at all.
So if you try to feed a non-NZB (for example: a .PDF or .ISO file) to SABnzbd, it will say "WARNING: Empty NZB file". So you can read "WARNING: Empty NZB file" as "WARNING: Empty or no NZB file"
HTH