public function add($username, $repository, $issue, array $parameters)
    {
        if (!isset($parameters['assignees'])) {
            throw new MissingArgumentException('assignees');
        }

        if (!is_array($parameters['assignees'])) {
            @trigger_error(sprintf('Passing the "assignees" parameter as a string in "%s" is deprecated and will throw an exception in php-github-api version 3.0. Pass an array of strings instead', __METHOD__), E_USER_DEPRECATED);

            $parameters['assignees'] = [$parameters['assignees']];
        }

        return $this->post('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/issues/'.rawurlencode($issue).'/assignees', $parameters);
    }