code: func (spec *Spec) IsKubeletExpandable() bool {
  	switch {
  	case spec.Volume != nil:
  		return spec.Volume.FlexVolume != nil
  	case spec.PersistentVolume != nil:
  		return spec.PersistentVolume.Spec.FlexVolume != nil
  	default:
  		return false
  
  	}
  }
docs: // IsKubeletExpandable returns true for volume types that can be expanded only by the node
  // and not the controller. Currently Flex volume is the only one in this category since
  // it is typically not installed on the controller