docs: public String getMessageCode(BaseMessage externalMessage)
      {
          if (!(externalMessage.getExternalMessage() instanceof ServiceTrxMessageIn))
              return null;
          Object message = externalMessage.getExternalMessage().getRawData();
          if (message != null)
              return "OTA_" + message.getClass().getSimpleName();
          return null;    // No type found.
      }