code: func AddToJournal(c context.Context, m ...Mutation) error {
  	(logging.Fields{"count": len(m)}).Infof(c, "tumble.AddToJournal")
  	if len(m) == 0 {
  		return nil
  	}
  	return RunMutation(c, addToJournalMutation(m))
  }
docs: // AddToJournal records one or more Mutation to the tumble journal, but does not
  // execute any of them. This does so by running a transaction on a pseudo-random
  // entity group, and journaling the mutations there.