#vulnerable code 
                                public void createX509CertClient(PrivateKey privatekey, Certificate[] trustedCertificates) {
        ObjectsInitializer initializer = new ObjectsInitializer();
        // TODO security instance with certificate info
        initializer.setInstancesForObject(LwM2mId.SECURITY, Security.noSec(
                "coaps://" + server.getSecureAddress().getHostString() + ":" + server.getSecureAddress().getPort(),
                12345));
        initializer.setInstancesForObject(LwM2mId.SERVER, new Server(12345, LIFETIME, BindingMode.U, false));
        initializer.setInstancesForObject(LwM2mId.DEVICE, new Device("Eclipse Leshan", MODEL_NUMBER, "12345", "U"));
        List<LwM2mObjectEnabler> objects = initializer.createMandatory();
        objects.add(initializer.create(2));

        InetSocketAddress clientAddress = new InetSocketAddress(InetAddress.getLoopbackAddress(), 0);
        DtlsConnectorConfig.Builder config = new DtlsConnectorConfig.Builder().setAddress(clientAddress);
        // TODO we should read the config from the security object
        config.setIdentity(privatekey, clientX509CertChain, false);
        config.setTrustStore(trustedCertificates);

        CoapServer coapServer = new CoapServer();
        coapServer.addEndpoint(new CoapEndpoint(new DTLSConnector(config.build()), NetworkConfig.getStandard()));

        LeshanClientBuilder builder = new LeshanClientBuilder(getCurrentEndpoint());
        builder.setLocalAddress(clientAddress.getHostString(), clientAddress.getPort());
        builder.setObjects(objects);
        client = builder.build();
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public void createX509CertClient(PrivateKey privatekey, Certificate[] trustedCertificates) {
        ObjectsInitializer initializer = new ObjectsInitializer();
        // TODO security instance with certificate info
        initializer.setInstancesForObject(LwM2mId.SECURITY, Security.noSec(
                "coaps://" + server.getSecuredAddress().getHostString() + ":" + server.getSecuredAddress().getPort(),
                12345));
        initializer.setInstancesForObject(LwM2mId.SERVER, new Server(12345, LIFETIME, BindingMode.U, false));
        initializer.setInstancesForObject(LwM2mId.DEVICE, new Device("Eclipse Leshan", MODEL_NUMBER, "12345", "U"));
        List<LwM2mObjectEnabler> objects = initializer.createMandatory();
        objects.add(initializer.create(2));

        InetSocketAddress clientAddress = new InetSocketAddress(InetAddress.getLoopbackAddress(), 0);
        DtlsConnectorConfig.Builder config = new DtlsConnectorConfig.Builder().setAddress(clientAddress);
        // TODO we should read the config from the security object
        config.setIdentity(privatekey, clientX509CertChain, false);
        config.setTrustStore(trustedCertificates);

        CoapServer coapServer = new CoapServer();
        coapServer.addEndpoint(new CoapEndpoint(new DTLSConnector(config.build()), NetworkConfig.getStandard()));

        LeshanClientBuilder builder = new LeshanClientBuilder(getCurrentEndpoint());
        builder.setLocalAddress(clientAddress.getHostString(), clientAddress.getPort());
        builder.setObjects(objects);
        client = builder.build();
    }