code: func (s *Server) loadNodeID() string {
  	if s.nodeID != "" {
  		return s.nodeID
  	}
  	nodeID, err := s.holder.loadNodeID()
  	if err != nil {
  		s.logger.Printf("loading NodeID: %v", err)
  		return s.nodeID
  	}
  	return nodeID
  }
docs: // loadNodeID gets NodeID from disk, or creates a new value.
  // If server.NodeID is already set, a new ID is not created.