() ->
              Stream.of(immutableCell("one", "uno", 1), immutableCell("one", "uno", (Integer) null))
                  .collect(collector));
    }
  }

  public void testToImmutableTableMerging() {
    Collector<Cell<String, String, Integer>, ?, ImmutableTable<String, String, Integer>> collector =
        toImmutableTable(Cell::getRowKey, Cell::getColumnKey, Cell::getValue, Integer::sum);