code: public static JustificationBuilder getInstance() {
  
      if (instance == null) {
        synchronized (JustificationBuilderImpl.class) {
          if (instance == null) {
            instance = new JustificationBuilderImpl();
          }
        }
      }
      return instance;
    }
docs: This method gets the singleton instance of this {@link JustificationBuilder}. <br>
  <b>ATTENTION:</b><br>
  Please prefer dependency-injection instead of using this method.
  
  @return the singleton instance.