assertThrows(
        NullPointerException.class,
        () -> Stream.of((Cell<String, String, Integer>) cell).collect(collector));
  }

  public void testToTableConflict() {
    Collector<Cell<String, String, Integer>, ?, Table<String, String, Integer>> collector =
        TableCollectors.toTable(
            Cell::getRowKey, Cell::getColumnKey, Cell::getValue, HashBasedTable::create);