drop down list 'append_items'

When I try to append an item to a drop down list It fails with an error
message....

item cannot be undef at ... etc etc

A snippet of my code is below. The print statement works fine so I know
that $entry_text is available for use. In fact, if I change this to
append_items("Some Text") it still fails!?


$button_add->signal_connect( "clicked", \&add_entry, $entry, $combo );

sub add_entry
{
    my ( $widget, $entry, $combo ) = @_;
    my $entry_text = $entry->get_text();
    print "Entry contents: $entry_text\n";
    $combo->list->append_items($entry_text);
}

Any ideas!?

Thanks

-- 
Andy Ford