code: public E getBest(int threshold) {
  
      E best = null;
      int bestRank = threshold - 1;
      for (E element : this.map.keySet()) {
        Ranking ranking = this.map.get(element);
        if (ranking != null) {
          if (ranking.rank > bestRank) {
            best = element;
            bestRank = ranking.rank;
          }
        }
      }
      return best;
    }
docs: This method gets the element that has currently the best (highest) {@link #getRank(Object) rank} greater or equal
  to the given {@code threshold}. If there are multiple best elements, it is unspecified which one is returned.
  
  @see #getBests()
  
  @param threshold is the minimum rank accepted for the best element.
  @return the element with the best rank greater or equal to the given {@code threshold} or {@code null} if there is
  no such element.