code: public void validate() throws ValidationException {
          super.validate();
  
          if (getDate() != null && !(getDate() instanceof DateTime)) {
              throw new ValidationException(
                      "Property must have a DATE-TIME value");
          }
  
          final DateTime dateTime = (DateTime) getDate();
  
          if (dateTime != null && !dateTime.isUtc()) {
              throw new ValidationException(getName() +
                      ": DATE-TIME value must be specified in UTC time");
          }
      }
docs: {@inheritDoc}