code: private static Tuple3<Set<Object>, Set<PathSpec>, Boolean> reduceContainsBatch(Tuple3<Set<Object>, Set<PathSpec>, Boolean> state,
        Request<?> request) {
      if (request instanceof GetRequest) {
        return state;
      } else if (request instanceof BatchRequest) {
        return Tuples.tuple(state._1(), state._2(), true);
      } else {
        throw unsupportedGetRequestType(request);
      }
    }
docs: Tuple3: (keys, fields, contains-batch-get)