Basically your generate subroutine would look like:

sub generate {
  my $hashref = shift;
  my $template = HTML::Template->new(filename => "$tmpldir/generic.tt"
+);
  $template->param(map { defined $hashref->{$_} ? ($_ => $hashref->{$_
+}) : ()  } 
          keys %$hashref);

   );
   print $template->output;
}
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This works because HTML::Template::param expects a list an even number of elements in length suitable for hash type operations, and map of course produces lists, so our expression there utilizes the ternary operator (?:) to test for defined values and outputs key/value pairs.

I am not really qualified to give advice about template design since I'm new to it myself. But just the fact you're using them I can comfortably say is a good sign :)

Many thanks, djantzen!

I like the map code because it's much flexible than having to specify the values to be passed to Template's param().

It's now working as expected :)