code: private ProjectCalendar getTaskCalendar(Project.Tasks.Task task)
     {
        ProjectCalendar calendar = null;
  
        BigInteger calendarID = task.getCalendarUID();
        if (calendarID != null)
        {
           calendar = m_projectFile.getCalendarByUniqueID(Integer.valueOf(calendarID.intValue()));
        }
  
        return (calendar);
     }
docs: This method is used to retrieve the calendar associated
  with a task. If no calendar is associated with a task, this method
  returns null.
  
  @param task MSPDI task
  @return calendar instance