code: private List<Date> getOffsetDates(final DateList dates, final int offset) {
          if (offset == 0) {
              return dates;
          }
          final List<Date> offsetDates = Dates.getDateListInstance(dates);
          final int size = dates.size();
          if (offset < 0 && offset >= -size) {
              offsetDates.add(dates.get(size + offset));
          } else if (offset > 0 && offset <= size) {
              offsetDates.add(dates.get(offset - 1));
          }
          return offsetDates;
      }
docs: Returns a single-element sublist containing the element of <code>list</code> at <code>offset</code>. Valid
  offsets are from 1 to the size of the list. If an invalid offset is supplied, all elements from <code>list</code>
  are added to <code>sublist</code>.
  
  @param dates
  @param offset