docs: public Summary toSummary(List<Keyword> keywords) {
  
          if (keywords == null) {
              keywords = new ArrayList<>();
          }
  
          if (keywords.isEmpty()) {
  
              KeyWordComputer kc = new KeyWordComputer(10);
              keywords = kc.computeArticleTfidf(title, content);
          }
          return explan(keywords, content);
      }