multimap.put("one", 1);
    multimap.put("two", 2);
    multimap.put("two", 22);
    multimap.put("three", 3);
    multimap.put("three", 33);
    multimap.put("three", 333);
  }

  @Override
  protected String getKeyNotInPopulatedMap() throws UnsupportedOperationException {
    return "zero";
  }

  @Override