#vulnerable code 
                                private void executeAttackRound(ConfigHandler configHandler) {
        TlsConfig tlsConfig = configHandler.initialize(config);
        LOGGER.info("Testing {}, {}", tlsConfig.getHighestProtocolVersion(), tlsConfig.getSupportedCiphersuites().get(0));

        TransportHandler transportHandler = configHandler.initializeTransportHandler(tlsConfig);
        TlsContext tlsContext = configHandler.initializeTlsContext(tlsConfig);
        WorkflowExecutor workflowExecutor = configHandler.initializeWorkflowExecutor(transportHandler, tlsContext);

        WorkflowTrace trace = tlsContext.getWorkflowTrace();

        FinishedMessage finishedMessage = (FinishedMessage) trace
                .getFirstConfiguredSendMessageOfType(HandshakeMessageType.FINISHED);
        Record record = createRecordWithBadPadding();
        finishedMessage.addRecord(record);

        // Remove last two server messages (CCS and Finished). Instead of them,
        // an alert will be sent.
        AlertMessage alertMessage = new AlertMessage(tlsConfig);

        ReceiveAction action = (ReceiveAction) (trace.getLastMessageAction());
        List<ProtocolMessage> messages = new LinkedList<>();
        messages.add(alertMessage);
        action.setConfiguredMessages(lastMessages);
        try {
            workflowExecutor.executeWorkflow();
        } catch (WorkflowExecutionException ex) {
            LOGGER.info("Not possible to finalize the defined workflow: {}", ex.getLocalizedMessage());
        }

        ProtocolMessage lm = trace.getLastConfiguredReceiveMesssage();
        lastMessages.add(lm);
        tlsContexts.add(tlsContext);

        if (lm.getProtocolMessageType() == ProtocolMessageType.ALERT) {
            AlertMessage am = ((AlertMessage) lm);
            LOGGER.info("  Last protocol message: Alert ({},{}) [{},{}]", AlertLevel.getAlertLevel(am.getLevel()
                    .getValue()), AlertDescription.getAlertDescription(am.getDescription().getValue()), am.getLevel()
                    .getValue(), am.getDescription().getValue());
        } else {
            LOGGER.info("  Last protocol message: {}", lm.getProtocolMessageType());
        }

        if (lm.getProtocolMessageType() == ProtocolMessageType.ALERT
                && ((AlertMessage) lm).getDescription().getValue() == 22) {
            LOGGER.info("  Vulnerable");
            vulnerable = true;
        } else {
            LOGGER.info("  Not Vulnerable / Not supported");
        }

        transportHandler.closeConnection();
    } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private void executeAttackRound(ConfigHandler configHandler) {
        TlsConfig tlsConfig = configHandler.initialize(config);
        LOGGER.info("Testing {}, {}", tlsConfig.getHighestProtocolVersion(), tlsConfig.getSupportedCiphersuites()
                .get(0));

        TransportHandler transportHandler = configHandler.initializeTransportHandler(tlsConfig);
        TlsContext tlsContext = configHandler.initializeTlsContext(tlsConfig);
        WorkflowExecutor workflowExecutor = configHandler.initializeWorkflowExecutor(transportHandler, tlsContext);

        WorkflowTrace trace = tlsContext.getWorkflowTrace();

        FinishedMessage finishedMessage = (FinishedMessage) trace
                .getFirstConfiguredSendMessageOfType(HandshakeMessageType.FINISHED);
        Record record = createRecordWithBadPadding();
        finishedMessage.addRecord(record);

        // Remove last two server messages (CCS and Finished). Instead of them,
        // an alert will be sent.
        AlertMessage alertMessage = new AlertMessage(tlsConfig);

        ReceiveAction action = (ReceiveAction) (trace.getLastMessageAction());
        List<ProtocolMessage> messages = new LinkedList<>();
        messages.add(alertMessage);
        action.setConfiguredMessages(lastMessages);
        try {
            workflowExecutor.executeWorkflow();
        } catch (WorkflowExecutionException ex) {
            LOGGER.info("Not possible to finalize the defined workflow: {}", ex.getLocalizedMessage());
        }

        ProtocolMessage lm = trace.getLastConfiguredReceiveMesssage();
        lastMessages.add(lm);
        tlsContexts.add(tlsContext);

        if (lm.getProtocolMessageType() == ProtocolMessageType.ALERT) {
            AlertMessage am = ((AlertMessage) lm);
            LOGGER.info("  Last protocol message: Alert ({},{}) [{},{}]", AlertLevel.getAlertLevel(am.getLevel()
                    .getValue()), AlertDescription.getAlertDescription(am.getDescription().getValue()), am.getLevel()
                    .getValue(), am.getDescription().getValue());
        } else {
            LOGGER.info("  Last protocol message: {}", lm.getProtocolMessageType());
        }

        if (lm.getProtocolMessageType() == ProtocolMessageType.ALERT
                && ((AlertMessage) lm).getDescription().getValue() == 22) {
            LOGGER.info("  Vulnerable");
            vulnerable = true;
        } else {
            LOGGER.info("  Not Vulnerable / Not supported");
        }

        transportHandler.closeConnection();
    }