code: public static String formatJsonDate(Instant value) {
          if (value == null) {
              return null;
          }
          return JSON_DATETIME_FORMAT.format(value.atOffset(ZoneOffset.UTC));
      }
docs: Formats a time instant as ISO8601 in UTC with millisecond precision, e.g. "2014-10-03T09:41:12.790Z"