add message to door locked event

src/main/java/application/events/impl/DoorLockedEvent.java

@@ -27,7 +27,7 @@ public class DoorLockedEvent implements EventObject {
 
     @Override
     public String createMessage() {
-        return null;
+        return "Door " + user +  "locked, because" + reason;
     }
 
     @Id