docs: public int compareTo(WordTag wordTag) {    
      int first = (word != null ? word().compareTo(wordTag.word()) : 0);
      if(first != 0)
        return first;
      else {
        if (tag() == null) {
          if (wordTag.tag() == null)
            return 0;
          else
            return -1;
        }
        return tag().compareTo(wordTag.tag());
      }
    }