dispatch_address_postcode

zorunlu değildir ve o hala boş olsa bile çalışacaktır:

if (!is_null($_POST['personal_info_first_name']) && 
    !is_null($_POST['personal_info_surname']) && 
    !is_null($_POST['personal_info_email']) && 
    !is_null($_POST['personal_info_telephone']) && 
    !is_null($_POST['dispatch_address_country']) && 
    !is_null($_POST['dispatch_address_first_name']) &&
    !is_null($_POST['dispatch_address_surname']) && 
    !is_null($_POST['dispatch_address_address']) && 
    !is_null($_POST['dispatch_address_town']) && 
    !is_null($_POST['dispatch_address_postcode']) && 
    !is_null($_POST['dispatch_address_county']) && 
    (   ($_POST['payment_method'] == "Pay by credit card.") ||
        (
            ($_POST['payment_method'] == "Pay by new credit card.") && 
            !is_null($_POST['card_number']) && 
            !is_null($_POST['expiration_date']) && 
            !is_null($_POST['security_code'])
        )
    )
)

Ne verir?