code: protected String getMessage(final SmsSendRequestDto smsSendRequestDto) {
      if (StringUtils.isNotBlank(smsSendRequestDto.getMessage())) {
        return smsSendRequestDto.getMessage();
      }
      Validate.notEmpty(defaultMessage, "defaultMessage must not be null or blank");
      return defaultMessage;
    }
docs: Returns the message of the request. If no message is specified the default message will be
  returned.
  
  @param smsSendRequestDto the sms request
  @return the message
  @throws IllegalArgumentException if no message is specified at all