code: func (group *NodeGroup) SetNodes(nodes ...Node) []Node {
  	if group == nil {
  		return nil
  	}
  
  	group.mux.Lock()
  	defer group.mux.Unlock()
  
  	old := group.nodes
  	group.nodes = nodes
  	return old
  }
docs: // SetNodes replaces the group nodes to the specified nodes,
  // and returns the previous nodes.