code: func New(oauthClient *http.Client, parentID string) (*DriveService, error) {
  	apiservice, err := client.New(oauthClient)
  	if err != nil {
  		return nil, err
  	}
  	if parentID == "" {
  		// because "root" is known as a special alias for the root directory in drive.
  		parentID = "root"
  	}
  	service := &DriveService{client: oauthClient, apiservice: apiservice, parentID: parentID}
  	return service, err
  }
docs: // New initiates a new DriveService. parentID is the ID of the directory
  // that will be used as the current directory in methods on the returned
  // DriveService (such as Get). If empty, it defaults to the root of the
  // drive.