code: func (nDB *NetworkDB) addNetworkNode(nid string, nodeName string) {
  	nodes := nDB.networkNodes[nid]
  	for _, node := range nodes {
  		if node == nodeName {
  			return
  		}
  	}
  
  	nDB.networkNodes[nid] = append(nDB.networkNodes[nid], nodeName)
  }
docs: // addNetworkNode adds the node to the list of nodes which participate
  // in the passed network only if it is not already present. Caller
  // should hold the NetworkDB lock while calling this