protected void append(LoggingEvent event) {
    // No op. We're just using the appender as a convenient way to start the
    // JmxServer without introducing any dependencies anywhere for Log4J.
  }
Calling the default constructor causes this appender to register JmxLog4J
as a JMX MBean.

@param mbeanServer to be injected for unit testing.
samza-log4j/src/main/java/org/apache/samza/logging/log4j/JmxAppender.java