@Test
    public void testGroupedWithNullClassifications() throws Exception {
        List<Tuple2<Integer, List<Integer>>> list =
        Seq.of(1, 2, 3, 4)
           .grouped(x -> x % 2 == 0 ? null : 1)
           .map(kv -> kv.map2(cls -> cls.toList())).toList();

        assertEquals(asList(
            Tuple.tuple(1, Arrays.asList(1, 3)),
            Tuple.tuple(null, Arrays.asList(2, 4))
        ), list);
    }
@author Lukas Eder
@author Roman Tkalenko
jOOL-java-8/src/test/java/org/jooq/lambda/SeqTest.java