Форум

\Bitrix\Main\EventManager::getInstance()->addEventHandlerCompatible('sale', 
    'OnSaleComponentOrderProperties',
    'SaleOrderEvents::fillLocation'
);

class SaleOrderEvents {

    function fillLocation(&$arUserResult, $request, &$arParams, &$arResult) 
    {
        $registry = \Bitrix\Sale\Registry::getInstance(\Bitrix\Sale\Registry::REGISTRY_TYPE_ORDER);
        $orderClassName = $registry->getOrderClassName();
        $order = $orderClassName::create(\Bitrix\Main\Application::getInstance()->getContext()->getSite());
        $propertyCollection = $order->getPropertyCollection();
        foreach ($propertyCollection as $property)
        {
            if($property->isUtil()) continue;
            $arProperty = $property->getProperty();
            if($arProperty['TYPE'] === 'LOCATION' 
                && array_key_exists($arProperty['ID'],$arUserResult["ORDER_PROP"])
                && !$request->getPost("ORDER_PROP_".$arProperty['ID'])
                && (
                    !is_array($arOrder=$request->getPost("order"))
                    || !$arOrder["ORDER_PROP_".$arProperty['ID']]
                )
            ){
                $arUserResult["ORDER_PROP"][$arProperty['ID']] = CURRENT_CITY_CODE;
            }
        }
    }
}