code: func buildNodeIDMapFromAnnotation(node *v1.Node) (map[string]string, error) {
  	var previousAnnotationValue string
  	if node.ObjectMeta.Annotations != nil {
  		previousAnnotationValue =
  			node.ObjectMeta.Annotations[annotationKeyNodeID]
  	}
  
  	var existingDriverMap map[string]string
  	if previousAnnotationValue != "" {
  		// Parse previousAnnotationValue as JSON
  		if err := json.Unmarshal([]byte(previousAnnotationValue), &existingDriverMap); err != nil {
  			return nil, fmt.Errorf(
  				"failed to parse node's %q annotation value (%q) err=%v",
  				annotationKeyNodeID,
  				previousAnnotationValue,
  				err)
  		}
  	}
  
  	if existingDriverMap == nil {
  		return make(map[string]string), nil
  	}
  	return existingDriverMap, nil
  }
docs: // Guarantees the map is non-nil if no error is returned.