code: private void addExceptionRange(ProjectCalendarException exception, Date start, Date finish)
     {
        if (start != null && finish != null)
        {
           exception.addRange(new DateRange(start, finish));
        }
     }
docs: Add a range to an exception, ensure that we don't try to add null ranges.
  
  @param exception target exception
  @param start exception start
  @param finish exception finish