docs: public Object scheduleAt(final Date date,
                               final Runnable runnable)
                               throws IllegalArgumentException {
  
          if (date == null) {
              throw new IllegalArgumentException("date == null");
          } else if (runnable == null) {
              throw new IllegalArgumentException("runnable == null");
          }
  
          return this.addTask(date.getTime(), runnable, 0, false);
      }