code: func (t *SessionTimers) Set(id string, tm *time.Timer) {
  	t.Lock()
  	defer t.Unlock()
  	if tm == nil {
  		delete(t.m, id)
  	} else {
  		t.m[id] = tm
  	}
  }
docs: // Set stores the timer under given id. If tm is nil the timer
  // with the given id is removed.