code: func (client *GCSBlobstore) Exists(dest string) (exists bool, err error) {
  	if exists, err = client.exists(client.publicGCS, dest); err == nil {
  		return exists, nil
  	}
  
  	// If the public client fails, try using it as an authenticated actor
  	if client.authenticatedGCS != nil {
  		return client.exists(client.authenticatedGCS, dest)
  	}
  
  	return
  }
docs: // Exists checks if a blob exists in the GCS blobstore.