private void setMessage() {
    if (!_exceptionChain.isEmpty()) {
      this._message = _exceptionChain.get(0).getMessage();
    }
  }
Sets message for the logging event
  For now, It is set to be equal to the message field of first EventException in _exceptionChain
  This can be changed depending on message of which EventException is most relevant for the user to see
app/com/linkedin/drelephant/exceptions/LoggingEvent.java