anchor.diff:  To avoid forgetting to do housekeeping afterwards, we can use a try-with-resource construct:
   [source,java]
   ----
  -try(MDC.MDCCloseable mdc = MDC.putCloseable("user", "gquintana")) {
  +try(MDC.MDCCloseable mdc = MDC.putCloseable("userId", "gquintana")) {
   	demoLogger.info("Hello world!");
   }
   ----
  
positive.code:     }
  }
  ----
  Several Maven dependencies are required: `ch.qos.logback.contrib:logback-json-classic:0.1.5`, `ch.qos.logback.contrib:logback-jackson:0.1.5` and `com.fasterxml.jackson.core:jackson-databind`.
  
negative.code: public class CustomJsonLayout extends JsonLayout {
      @Override
      protected void addCustomDataToJsonMap(Map<String, Object> map, ILoggingEvent event) {
          map.put("application", "log-odyssey");
          try {
              map.put("host", InetAddress.getLocalHost().getHostName());
          } catch (UnknownHostException e) {
  