code: func (nt *NodeTree) UpdateNode(old, new *v1.Node) {
  	var oldZone string
  	if old != nil {
  		oldZone = utilnode.GetZoneKey(old)
  	}
  	newZone := utilnode.GetZoneKey(new)
  	// If the zone ID of the node has not changed, we don't need to do anything. Name of the node
  	// cannot be changed in an update.
  	if oldZone == newZone {
  		return
  	}
  	nt.mu.Lock()
  	defer nt.mu.Unlock()
  	nt.removeNode(old) // No error checking. We ignore whether the old node exists or not.
  	nt.addNode(new)
  }
docs: // UpdateNode updates a node in the NodeTree.