... code to setup my $t template, and get
info from the database into %fdat
would be here ...

   my $html = $t->output;
   if ( %fdat ) {
      my $fif = new HTML::FillInForm;
      $html = $fif->fill(scalarref  => \$html,
                          fdat   =>  \%fdat );
   }

   return $html;  # this is the filled-out HTML file