Distinct implements CombinerAggregator<Set<Integer>> { @Override public Set<Integer> zero() { return new HashSet<Integer>(); }  @Override Set<Integer> init(TridentTuple tuple); @Override Set<Integer> combine(Set<Integer> val1, Set<Integer> val2); @Override Set<Integer> zero();  }
@Test public void testZero() throws Exception { assertThat(distinct.zero()) .isNotNull() .isInstanceOf(HashSet.class) .isEmpty(); }