Could not connect to device: NullPointerException connecting from android to Zebra printer via USB?

Question

am trying to connect to a Zebra Printer, model ZDesigner GK420t, from an Android Application via USB using the new UsbConnection(), where the parameters assigned to USBConnection() constructor are as follows:

            UsbManager manager = (UsbManager) mContext.getSystemService(Context.USB_SERVICE);
        HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
        String DeviceName = "";
        for (String s : deviceList.keySet()) {
            DeviceName = s;
            break;
        }
        UsbDevice device = deviceList.get(DeviceName);
        connection = new UsbConnection(manager, device);
        connection.open();

However, the connection.Open() is causing the following Exception:

Exception Message: Could not connect to device: NullPointerException
Exception Class: com.zebra.sdk.comm.ConnectionException
Cause: java.lang.NullPointerException

What I tried so far to make sure that the assigned parameters as UsbManager and USB Device are not being handled to the UsbConnection() as Nulls is appending Toasts before the connection.Open() as follows, where the Toasts printed respectively "manager", "device":

Toast.makeText(mContext, manager == null ? "null manager" : "manager", Toast.LENGTH_LONG).show();
        Toast.makeText(mContext, device == null ? "null device" : "device", Toast.LENGTH_LONG).show();

Also made sure that the connection instantiated is not null by appending the Toast before connection.Open(), as follows, where the Toast printed connection:

Toast.makeText(mContext, connection == null ? "null connection== " : "connection", Toast.LENGTH_LONG).show();

Important Note: The property connectionAttributes of the "connection" object is being retrieved as null, one time the connectionAttribute property was assigned value of "Map" with length of 7, and the printer printed the buffer, trying to collect data about what was different during this connection.open() call when the connectionAttributes value was not retrieved as null.

Can't figure out what is causing the NullPointerException

Please help!