protected function buildDefaultItemRow()
{
$row = parent::buildDefaultItemRow();
// remove old fileds
unset($row["unit_amount"]);
unset($row["old_unit_amount"]);
unset($row["tax_percent"]);
$newFields = array("tax_class" => "", "unit_amount_net" => "0", "old_unit_amount_net" => "");
$row = array_slice($row, 0, 3, true) + $newFields + array_slice($row, 3, count($row) - 3, true);
return $row;
}
