[Demonstration 1]

[Buggy Method]
public void changeTaskDate(Long taskID, Date dateOfTask) {
    CalibrationTask task = taskRepository.findOne(taskID);
    if (task == null || dateOfTask == null) {
        throw new IllegalArgumentException();
    }
    task.setDateOfTask(dateOfTask);
    try {
        taskRepository.save(task);
    } catch (Exception e) {
        throw new IllegalArgumentException();
    }
}

[Buggy Hunk]
throw new IllegalArgumentException();

[Patch]
throw new IllegalArgumentException(e);

[Demonstration 2]

[Buggy Method]
public String insertARI(ApplicationReqIdentifier ari) {
    String ariJson = "{ " + "'userId': '" + ari.getUserId() + "'," + "'appId': '" + ari.getUserId() + "'," + "'services' : " + "{general : { " + "precondition: 'AppName'," + "feature: '" + ari.getGeneralARI().getAppName() + "'}" + "}}";
    DBObject dbObject = (DBObject) JSON.parse(ariJson);
    DB db = MongoDB.getMongoConnection("local");
    DBCollection collection = db.getCollection("ari");
    collection.insert(dbObject);
    ObjectId id = (ObjectId) dbObject.get("_id");
    System.out.println(id.toString());
    return id.toString();
}

[Buggy Hunk]
System.out.println(id.toString());

[Patch]
System.out.println("inside ARI_Dao class; arid id = " + id.toString());

[Demonstration 3]

[Buggy Method]
@RequestMapping(value = { "/edituser.html", "/edituser.html{?id=}" }, method = RequestMethod.GET)
public ModelAndView editUserFormGet(@RequestParam(value = "id", required = false) String id) {
    ModelAndView model = new ModelAndView("editUser");
    if (id != null) {
        User u = new User();
        startMongoSession();
        MongoUserDAO uDAO = new MongoUserDAO(mongo.getInstance());
        u = uDAO.getUserById(new ObjectId(id));
        model.addObject("username", u.getUsername());
        model.addObject("firstName", u.getFirstName());
        model.addObject("lastName", u.getLastName());
        mongo.close();
        userId = id;
    }
    return model;
}

[Buggy Hunk]
u = uDAO.getUserById(new ObjectId(id));

[Patch]
u = uDAO.getUser(new ObjectId(id));