code: public ProjectCalendarException addCalendarException(Date fromDate, Date toDate)
     {
        ProjectCalendarException bce = new ProjectCalendarException(fromDate, toDate);
        m_exceptions.add(bce);
        m_expandedExceptions.clear();
        m_exceptionsSorted = false;
        clearWorkingDateCache();
        return bce;
     }
docs: Used to add exceptions to the calendar. The MPX standard defines
  a limit of 250 exceptions per calendar.
  
  @param fromDate exception start date
  @param toDate exception end date
  @return ProjectCalendarException instance