@Test
public void testDistinctIsNullSafe() throws Exception {
DataBag empty = bagFactory.newDefaultBag();
Tuple tupleOfNull = tupleFactory.newTuple(1);
Tuple tupleOfEmpty = tupleFactory.newTuple(empty);
assertEquals(empty, new Distinct().exec(tupleOfNull));
assertEquals(tupleOfEmpty, new Distinct.Initial().exec(tupleOfNull));
assertEquals(tupleOfEmpty, new Distinct.Intermediate().exec(tupleOfNull));
assertEquals(empty, new Distinct.Final().exec(tupleOfNull));
}