if !exist {
	// 找不到, 从服务器获取
	user = newUser(msg.Owner(), msg.FromUserName)
	err = user.Detail()
	b.self.members = b.self.members.Append(user)
	b.self.groups = b.self.members.Groups()
}

users := groups.SearchByUserName(1, username)
if users.Count() == 0 {
	group := newUser(m.Owner(), username)
	if err := group.Detail(); err == nil {
		return group, nil
	}
	return nil, ErrNoSuchUserFoundError
}