Thanks for the response. A test, using something similar, indeed works.
It turns out that I had a different problem..
$cgi_vars{fname} was indeed being set to "", but later in the script it was re-set to an 'undefined' value. This, of course, was not readily discernible in my test print statements.

So this returned the original value if the $cgi_vars{fname} value is undefined.

$q->param('fname' => $cgi_vars{fname});
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