code: func (m *MountPoint) Cleanup() error {
  	if m.Volume == nil || m.ID == "" {
  		return nil
  	}
  
  	if err := m.Volume.Unmount(m.ID); err != nil {
  		return errors.Wrapf(err, "error unmounting volume %s", m.Volume.Name())
  	}
  
  	m.active--
  	if m.active == 0 {
  		m.ID = ""
  	}
  	return nil
  }
docs: // Cleanup frees resources used by the mountpoint