code: func (az *Cloud) GetUnmanagedNodes() (sets.String, error) {
  	// Kubelet won't set az.nodeInformerSynced, always return nil.
  	if az.nodeInformerSynced == nil {
  		return nil, nil
  	}
  
  	az.nodeCachesLock.Lock()
  	defer az.nodeCachesLock.Unlock()
  	if !az.nodeInformerSynced() {
  		return nil, fmt.Errorf("node informer is not synced when trying to GetUnmanagedNodes")
  	}
  
  	return sets.NewString(az.unmanagedNodes.List()...), nil
  }
docs: // GetUnmanagedNodes returns a list of nodes not managed by Azure cloud provider (e.g. on-prem nodes).