function getDelta($cursor = null, $pathPrefix = null)
    {
        Checker::argStringNonEmptyOrNull("cursor", $cursor);
        Path::checkArgOrNull("pathPrefix", $pathPrefix);

        $response = $this->doPost($this->apiHost, "1/delta", array(
            "cursor" => $cursor,
            "path_prefix" => $pathPrefix));

        if ($response->statusCode !== 200) throw RequestUtil::unexpectedStatus($response);

        return RequestUtil::parseResponseJson($response->body);
    }