public function signRawTransaction($hex_data, array $prevtxs = [], array $priv_keys = [], $sighashtype = "ALL")
    {
        $args = [
            (string)$hex_data,
            !empty($prevtxs)   ? $prevtxs   : null,
            !empty($priv_keys) ? $priv_keys : null,
            (string)$sighashtype
        ];
        return $this->rpc->query(__FUNCTION__, $args);
    }