code: func getRollbackTo(d *apps.Deployment) *extensions.RollbackConfig {
  	// Extract the annotation used for round-tripping the deprecated RollbackTo field.
  	revision := d.Annotations[apps.DeprecatedRollbackTo]
  	if revision == "" {
  		return nil
  	}
  	revision64, err := strconv.ParseInt(revision, 10, 64)
  	if err != nil {
  		// If it's invalid, ignore it.
  		return nil
  	}
  	return &extensions.RollbackConfig{
  		Revision: revision64,
  	}
  }
docs: // TODO: Remove this when extensions/v1beta1 and apps/v1beta1 Deployment are dropped.