code: public SearchCriteria addOrder(
                      final Order order
                      )
      {
          if (order == null) {
              throw new IllegalArgumentException( "no order specified" );
          }
  
          _orders.add( order );
  
          return this;
      }
docs: Appends the specified ordering criterion.
  
  @param   order
  the ordering criterion.
  @throws  NullPointerException
  if the argument is null.