Hub.java (with jpf-symbc):
1. protected static Logger log = null; //LoggerFactory.getLogger(edu.duke.cs.legosdn.tests.apps.hub.Hub.class);
2. OFPacketIn pi =  (OFPacketIn) msg; // cannot convert OFMessage to OFPacketIn
3.             byte[] packetData = pi.getPacketData();
            po.setLength(U16.t(OFPacketOut.MINIMUM_LENGTH
                               + po.getActionsLength()  +  packetData.length)); // null pointer for packetData

AppLoader.java:
1. private static final Logger logger =  null;
        // LoggerFactory.getLogger(AppLoader.class);
2. private static final InetSocketAddress PROXY_ADDR = null; // cannot find native java.net.InetAddress.init
            // new InetSocketAddress(InetAddress.getLoopbackAddress(), Defaults.PROXY_PORT);
3. private static final ChannelFactory CPLANE_FACTORY = null; // java.lang.Error: java.lang.NoSuchFieldException: tid
            // new NioClientSocketChannelFactory(Executors.newFixedThreadPool(4),
            //                                   Executors.newFixedThreadPool(16));

Controller.java:
1. protected static final Logger log = null; // LoggerFactory.getLogger(Controller.class);
2.     protected static final INotificationManager notifier = null;
             // NotificationManagerFactory.getNotificationManager(Controller.class);
3. in handleMessage(): 
if (m.getType()!=null) // zzy: java.lang.NullPointerException: Calling 'ordinal()I' on null object
        switch (m.getType()) {