public function index($product_sku)
    {
        $product = Subbly::api('subbly.product')->find($product_sku);

        $options = $this->getParams('offset', 'limit', 'includes', 'order_by');

        $productImages = Subbly::api('subbly.product_image')->findByProduct($product, $options);

        return $this->jsonCollectionResponse('product_images', $productImages);
    }