code: protected String formatDate(DateIntervalType type, GroupStrategy strategy, String date, String pattern, String expression) {
          if (date == null) {
              return null;
          }
          String str = GroupStrategy.FIXED.equals(strategy) ? formatDateFixed(type, date) : formatDateDynamic(type, date, pattern);
          if (StringUtils.isBlank(expression)) {
              return str;
          }
          return getEvaluator().evalExpression(str, expression);
      }
docs: DATE FORMATTING