I guess I could dig into CGI.pm to see if my fears are unfounded with the current implementation and, also important, whether the documentation makes it clear that my fears should not become 'founded' in a future release of CGI.pm.

Your fears are unfounded both according to the source and the docs

To create an empty query, initialize it from an empty string or hash )

I remember this from source diving (which CGI.pm encourages) in the year 2000