immutableCell("one", "uno", 1),
            immutableCell("two", "dos", 2),
            immutableCell("three", "tres", 3),
            immutableCell("two", "dos", 4));
  }

  public void testToImmutableTableMergingNullRowKey() {
    Collector<Cell<String, String, Integer>, ?, ImmutableTable<String, String, Integer>> collector =
        TableCollectors.toImmutableTable(