@Nonnull
  @Override
  public Sketch<IntegerSummary> getResult() {
    return unionAll();
  }
@Test
  public void testUnionWithEmptyInput() {
    TupleIntSketchAccumulator accumulator = new TupleIntSketchAccumulator(_setOps, _nominalEntries, 3);
    TupleIntSketchAccumulator emptyAccumulator = new TupleIntSketchAccumulator(_setOps, _nominalEntries, 3);

    accumulator.merge(emptyAccumulator);

    Assert.assertTrue(accumulator.isEmpty());
    Assert.assertEquals(accumulator.getResult().getEstimate(), 0.0);
  }