code: public NewYearStrategy and(NewYearStrategy next) {
  
          List<NewYearStrategy> list = new ArrayList<>();
          list.addAll(this.strategies);
  
          if (list.isEmpty()) {
              list.add(this);
          }
  
          if (next.strategies.isEmpty()) {
              list.add(next);
          } else {
              list.addAll(next.strategies);
          }
  
          return new NewYearStrategy(list);
  
      }
docs: /*[deutsch]
  <p>Kombiniert diese und die angegebene Strategie zu einer neuen Strategie. </p>
  
  @param   next    strategy which chronologically follows after this strategy
  @return  combined stragegy
  @throws  IllegalArgumentException in case of multiple overlapping rules
  @since   3.14/4.11