Logback MDC test for empty key values

logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <variable scope="context" name="mdcPattern" value="%replace(emp:%X{emp} org:%X{org}){'[a-z]+:( |$)', ''}"/>
  <variable scope="context" name="logPattern" value="%-5p %d [%t] [${mdcPattern}] %c{20}: %m%n"/>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>${logPattern}</pattern>
    </encoder>
  </appender>

  <root level="DEBUG">
    <appender-ref ref="STDOUT" />
  </root>

</configuration>

LogbackMDCTest.java

package logogin.blogspot;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

/**
 * LogbackMDCTest.java
 *
 * @author logogin
 * @date Sep 3, 2014
 *
 */
public class LogbackMDCTest {

    private static final Logger logger = LoggerFactory.getLogger(LogbackMDCTest.class);

    public static void main(String ... args) {
        MDC.put("emp", "test_emp");
        MDC.put("org", "test_org");
        logger.info("This line should have MDC values");

        MDC.put("emp", "");
        MDC.put("org", "");
        logger.info("This line should have no empty MDC keys");
    }

}

System.out

INFO  2014-09-03 11:28:30,521 [main] [emp:test_emp org:test_org] l.b.LogbackMDCTest: This line should have MDC values
INFO  2014-09-03 11:28:30,526 [main] [] l.b.LogbackMDCTest: This line should have no empty MDC keys