code: protected String createResponseMessage(Exception e, String request, Object msgdoc, Map<String,String> metaInfo) {
          ListenerHelper helper = new ListenerHelper();
          if (e instanceof ServiceException)
              return helper.createErrorResponse(request, metaInfo, (ServiceException)e).getContent();
          else if (e != null)
              return helper.createErrorResponse(request, metaInfo, new ServiceException(ServiceException.INTERNAL_ERROR, e.getMessage())).getContent();
          else
              return helper.createAckResponse(request, metaInfo);
      }
docs: This method is used to create an MDW default response message. Such
  a message is only used when an exception occurred before customizable
  code is reached (e.g. the external message is malformed so we cannot
  determine which handler to call), or a simple acknowledgment is sufficient.
  
  @param e The exception that triggers the response message. This should be null
  if the message is for simple acknowledgment rather than for reporting an
  exception
  @param request request String
  @param msgdoc parsed object such XML Bean and JSON object if it is possible to parse the external message
  @param metaInfo protocol headers
  @return