code: private Integer getFrequency(Project.Calendars.Calendar.Exceptions.Exception exception)
     {
        Integer period = NumberHelper.getInteger(exception.getPeriod());
        if (period == null)
        {
           period = Integer.valueOf(1);
        }
        return period;
     }
docs: Retrieve the frequency of an exception.
  
  @param exception XML calendar exception
  @return frequency