protected function encode($data, $options = 0)
    {
        // Check is already json string.
        if (is_string($data) && strlen($data) >= 1) {
            $firstChar = $data[0];

            if (in_array($firstChar, ['[', '{', '"'])) {
                return $data;
            }
        }

        // Clear json_last_error()
        json_encode(null);

        $json = json_encode($data, $options);

        if (json_last_error() !== JSON_ERROR_NONE) {
            throw new \UnexpectedValueException(sprintf('JSON encode failure: %s', json_last_error_msg()));
        }

        return $json;
    }