Common logging pattern log.warn(null, ex) doesn't work

[radimk]

It is common to log exceptions without accompanying message like this:

    try {
      throw new IOException();
    } catch (Exception ex) {
      LOG.error(null, ex);
      throw new RuntimeException(ex);
    }

but the message is not processed by GELFJ. It is rejected by GelfMessage.isValid due to empty shortMessage field and while there is a test that seems to test this pattern is does not reveal the problem due to overriden behaviour in test sender.