table.put("a", 1, 'a');
    return table;
  }

  @Override
  protected Map<String, Map<Integer, Character>> makePopulatedMap() {
    TreeBasedTable<String, Integer, Character> table = makeTable();
    populateTable(table);
    return table.rowMap().tailMap("b");
  }

  @Override
  protected Map<String, Map<Integer, Character>> makeEmptyMap() {
    return makeTable().rowMap().tailMap("b");
  }

  @Override