code: @Nonnull
    public static GregorianCalendar getCalendar (@Nonnull final Date aDate)
    {
      final GregorianCalendar aCalendar = new GregorianCalendar (PDTFactory.getTimeZone (aDate),
                                                                 Locale.getDefault (Locale.Category.FORMAT));
      aCalendar.setTime (aDate);
      return aCalendar;
    }
docs: Get the passed date as {@link GregorianCalendar} using the default time
  zone.
  
  @param aDate
  The source date. May be <code>null</code>.
  @return Never <code>null</code>.