PayableShipmentItem::onFieldModify

protected function onFieldModify($name, $oldValue, $value)
{
	if ($name === 'QUANTITY')
	{
		if ($value !== 1)
		{
			$result = new Result();

			return $result->addError(
				new MainError(
					MainLocalizationLoc::getMessage('SALE_PAYABLE_ITEM_SHIPMENT_QUANTITY_ERROR')
				)
			);
		}
	}

	return parent::onFieldModify($name, $oldValue, $value);
}