One way to achieve this in your case would be to add a comment to the Category (edit a category, Tracks tab, add comment using the "..." button). So in the result category track source would be a folder with music and this comment. If a folder is empty, there's still a comment so no "Empty category" error message.
I'm surprised by your response because I thought it wasn't possible to add a comment to a category that already uses another source (folder, track, playlist, library, etc.).
For example, I configured a category with "Library" as the source and a comment (see my screenshot).
After several tests, the comment never appears in the playlist.
Whether the comment is at the top of the source list, whether or not there are "filters", "No Repeat," or "constraints".
The same applies when the source is a folder, a track, or a playlist.
The same applies when there's an error like: "
Unable to find track that fits criteria (rule: norepeat-track)."
That is, there will be no track selected from the category, and there will also be no comments in the playlist.
Tested on RadioBOSS 7.1.1.4
The only configuration that allows the comment to appear in the Playlist is when there is only one source: comment only.
As soon as there is an additional source, this prevents the comment from appearing.
Is this a bug, or did I misunderstand your answer?
And I said "I'm surprised" at the beginning of this message because I ran a similar test on a previous version of RadioBOSS and got the same result.
The only way for me to make a comment appear in the Playlist is to create a category just for a comment.