public function addDefaultRole($userId, $blogId = null)
    {

        //Get role (superadmin should always be administrator)
        if (is_super_admin($userId)) {
            $role = "administrator";
        } else {
            $role = $this->defaultRole;
        }

        //Check that user id is a valid int
        if (!is_numeric($userId)) {
            return false;
        }

        // Single
        if (is_numeric($blogId)) {
            if (is_user_member_of_blog($userId, $blogId) === true) {
                return false;
            }
            add_user_to_blog($blogId, $userId, $role);
            return true;
        }

        // Multiple
        if (is_null($blogId)) {
            foreach (get_sites() as $site) {
                if (is_user_member_of_blog($userId, $site->blog_id) === true) {
                    continue;
                }
                add_user_to_blog($site->blog_id, $userId, $role);
            }
        }

        return true;
    }