}
}
- if ($_SESSION['PO']->trans_type == ST_SUPPINVOICE && empty(trim(get_post('supp_ref'))))
+ if ($_SESSION['PO']->trans_type == ST_SUPPINVOICE && trim(get_post('supp_ref')) == false)
{
display_error(_("You must enter a supplier's invoice reference."));
set_focus('supp_ref');