protected function initializeStockItem(array $attr)
    {

        // load the stock item with the passed item/product/stock ID
        $entity = $this->loadStockItem(
            $attr[MemberNames::PRODUCT_ID],
            $attr[MemberNames::WEBSITE_ID],
            $attr[MemberNames::STOCK_ID]
        );

        // merge the attributes with the entity, if available
        if ($entity) {
            return $this->mergeEntity($entity, $attr);
        }

        // otherwise simply return the attributes
        return $attr;
    }