#fixed code
                                private byte[] processRequest(StunRequest request, InetSocketAddress localPeer, InetSocketAddress remotePeer)
            throws IOException {

        // Produce Binding Response
        TransportAddress transportAddress = new TransportAddress(remotePeer.getAddress(), remotePeer.getPort(), TransportProtocol.UDP);
        StunResponse response = StunMessageFactory.createBindingResponse(request, transportAddress);
        byte[] transactionID = request.getTransactionId();
        try {
            response.setTransactionID(transactionID);
        } catch (StunException e) {
            throw new IOException("Illegal STUN Transaction ID: " + new String(transactionID), e);
        }

        // The agent MUST use a short-term credential to authenticate the request and perform a message integrity check.
        UsernameAttribute remoteUnameAttribute = (UsernameAttribute) request.getAttribute(StunAttribute.USERNAME);;

        // Send binding error response if username is null
        if (remoteUnameAttribute.getUsername()==null) {
            response.setMessageType(StunMessage.BINDING_ERROR_RESPONSE);
            response.addAttribute(StunAttributeFactory.createErrorCodeAttribute(ErrorCodeAttribute.BAD_REQUEST,
                    ErrorCodeAttribute.getDefaultReasonPhrase(ErrorCodeAttribute.BAD_REQUEST)));
            return response.encode();
        }
        String remoteUsername = new String(remoteUnameAttribute.getUsername());

        // The agent MUST consider the username to be valid if it consists of two values separated by a colon, where the first
        // value is equal to the username fragment generated by the agent in an offer or answer for a session in-progress.
        if (!this.authenticator.validateUsername(remoteUsername)) {
            // TODO return error response
            throw new IOException("Invalid username " + remoteUsername);
        }

        // The username for the credential is formed by concatenating the username fragment provided by the peer with the
        // username fragment of the agent sending the request, separated by a colon (":").
        int colon = remoteUsername.indexOf(":");
        String localUFrag = remoteUsername.substring(0, colon);
        String remoteUfrag = remoteUsername.substring(colon + 1);

        // Add USERNAME and MESSAGE-INTEGRITY attribute in the response.
        // The responses utilize the same usernames and passwords as the requests.
        String localUsername = remoteUfrag.concat(":").concat(localUFrag);
        StunAttribute unameAttribute = StunAttributeFactory.createUsernameAttribute(localUsername);
        response.addAttribute(unameAttribute);

        byte[] localKey = this.authenticator.getLocalKey(localUFrag);
        MessageIntegrityAttribute integrityAttribute = StunAttributeFactory.createMessageIntegrityAttribute(remoteUsername,
                localKey);
        response.addAttribute(integrityAttribute);

        // If the client issues a USE-CANDIDATE, tell ICE Agent to select the candidate
        if (request.containsAttribute(StunAttribute.USE_CANDIDATE)) {
            if (!this.candidateSelected.get()) {
                this.candidateSelected.set(true);
                if (logger.isDebugEnabled()) {
                    logger.debug("Selected candidate " + remotePeer.toString());
                }
                this.iceListener.onSelectedCandidates(new SelectedCandidatesEvent(remotePeer));
            }
        }

        // Pass response to the server
        return response.encode();
    }
#vulnerable code 
                                private byte[] processRequest(StunRequest request, InetSocketAddress localPeer, InetSocketAddress remotePeer)
            throws IOException {

        // Produce Binding Response
        TransportAddress transportAddress = new TransportAddress(remotePeer.getAddress(), remotePeer.getPort(), TransportProtocol.UDP);
        StunResponse response = StunMessageFactory.createBindingResponse(request, transportAddress);
        byte[] transactionID = request.getTransactionId();
        try {
            response.setTransactionID(transactionID);
        } catch (StunException e) {
            throw new IOException("Illegal STUN Transaction ID: " + new String(transactionID), e);
        }

        // The agent MUST use a short-term credential to authenticate the request and perform a message integrity check.
        UsernameAttribute remoteUnameAttribute;
        String remoteUsername;
        // Send binding error response if username is null
        try {
            remoteUnameAttribute = (UsernameAttribute) request.getAttribute(StunAttribute.USERNAME);
            remoteUsername = new String(remoteUnameAttribute.getUsername());
        }
        catch(NullPointerException nullPointer) {
            response.setMessageType(StunMessage.BINDING_ERROR_RESPONSE);
            response.addAttribute(StunAttributeFactory.createErrorCodeAttribute(ErrorCodeAttribute.BAD_REQUEST,
                    ErrorCodeAttribute.getDefaultReasonPhrase(ErrorCodeAttribute.BAD_REQUEST)));
            return response.encode();
        } 

        // The agent MUST consider the username to be valid if it consists of two values separated by a colon, where the first
        // value is equal to the username fragment generated by the agent in an offer or answer for a session in-progress.
        if (!this.authenticator.validateUsername(remoteUsername)) {
            // TODO return error response
            throw new IOException("Invalid username " + remoteUsername);
        }

        // The username for the credential is formed by concatenating the username fragment provided by the peer with the
        // username fragment of the agent sending the request, separated by a colon (":").
        int colon = remoteUsername.indexOf(":");
        String localUFrag = remoteUsername.substring(0, colon);
        String remoteUfrag = remoteUsername.substring(colon + 1);

        // Add USERNAME and MESSAGE-INTEGRITY attribute in the response.
        // The responses utilize the same usernames and passwords as the requests.
        String localUsername = remoteUfrag.concat(":").concat(localUFrag);
        StunAttribute unameAttribute = StunAttributeFactory.createUsernameAttribute(localUsername);
        response.addAttribute(unameAttribute);

        byte[] localKey = this.authenticator.getLocalKey(localUFrag);
        MessageIntegrityAttribute integrityAttribute = StunAttributeFactory.createMessageIntegrityAttribute(remoteUsername,
                localKey);
        response.addAttribute(integrityAttribute);

        // If the client issues a USE-CANDIDATE, tell ICE Agent to select the candidate
        if (request.containsAttribute(StunAttribute.USE_CANDIDATE)) {
            if (!this.candidateSelected.get()) {
                this.candidateSelected.set(true);
                if (logger.isDebugEnabled()) {
                    logger.debug("Selected candidate " + remotePeer.toString());
                }
                this.iceListener.onSelectedCandidates(new SelectedCandidatesEvent(remotePeer));
            }
        }

        // Pass response to the server
        return response.encode();
    } 
                            #location 20 
                            #vulnerability type NULL_DEREFERENCE