code: func (s *server) GetSession(namespace string, id ID) (*Session, error) {
  	item, err := s.bk.Get(context.TODO(), activeKey(namespace, string(id)))
  	if err != nil {
  		if trace.IsNotFound(err) {
  			return nil, trace.NotFound("session(%v, %v) is not found", namespace, id)
  		}
  		return nil, trace.Wrap(err)
  	}
  	var sess Session
  	if err := json.Unmarshal(item.Value, &sess); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return &sess, nil
  }
docs: // GetSession returns the session by it's id. Returns NotFound if a session
  // is not found