Golang Mutation Update Not Returning Uid, but Does Commit

I have a mutation that updates an existing node. When I update with an existing uid, the api.Assigned struct does not have any uids returned, but does complete the update.

	input := &model{
   	     UID: "0x1234",
	        Name: "Test",
	}
	inputJson, err := json.Marshal(input)
	if err != nil {
		log.Println("error handing json marshal")
		return nil
	}

	mu := &api.Mutation{
		SetJson:   inputJson,
		CommitNow: true,
	}
	log.Println("mutation object:", mu)

	txn := o.graph.NewTxn()
	defer txn.Discard(ctx)
	assigned, err := txn.Mutate(ctx, mu)
	if err != nil {
		log.Println("error handing mutation for update")
		return nil
	}
	log.Println("assigned:", assigned.Uids)
	if _, ok := assigned.GetUids()[string(input.ID)]; !ok {
		log.Println("update unsuccessful")
		return nil
	}

The return of assigned.Uids is a blank map, but in the database, the Name has changed to “Test”. Is there something that I’m missing?