Firstly, move that code so it comes BEFORE the if (zen_not_null($_POST['address'])) { line.
And then change it so it reads:
Code:
if (isset($_POST['address']) && !zen_not_null($_POST['address'])) { //perform ALL checks on relevancy here
$messageStack->add_session($_GET['main_page'], TEXT_ERROR_VARIABLE_MISSING, 'error');
zen_redirect(zen_href_link($_GET['main_page']));
}
Absolute