code: func copyExistingContents(source, destination string) error {
  	dstList, err := ioutil.ReadDir(destination)
  	if err != nil {
  		return err
  	}
  	if len(dstList) != 0 {
  		// destination is not empty, do not copy
  		return nil
  	}
  	return fs.CopyDir(destination, source, ignoreUnsupportedXAttrs())
  }
docs: // copyExistingContents copies from the source to the destination and
  // ensures the ownership is appropriately set.