try {
      Stream.of(immutableCell("one", "uno", 1)).collect(collector);
      fail("Expected NullPointerException");
    } catch (NullPointerException expected) {
    }
    collector =
        TableCollectors.toImmutableTable(Cell::getRowKey, Cell::getColumnKey, Cell::getValue);
    try {
      Stream.of(immutableCell("one", "uno", 1), immutableCell("one", "uno", (Integer) null))
          .collect(collector);