code: func (nm *NamespaceController) syncNamespaceFromKey(key string) (err error) {
  	startTime := time.Now()
  	defer func() {
  		klog.V(4).Infof("Finished syncing namespace %q (%v)", key, time.Since(startTime))
  	}()
  
  	namespace, err := nm.lister.Get(key)
  	if errors.IsNotFound(err) {
  		klog.Infof("Namespace has been deleted %v", key)
  		return nil
  	}
  	if err != nil {
  		utilruntime.HandleError(fmt.Errorf("Unable to retrieve namespace %v from store: %v", key, err))
  		return err
  	}
  	return nm.namespacedResourcesDeleter.Delete(namespace.Name)
  }
docs: // syncNamespaceFromKey looks for a namespace with the specified key in its store and synchronizes it