'int java.io.InputStream.read(byte[])' on a null object reference while communicating with Bluetooth serial port

Question

I am trying to get serial port data via "Bluetooth". But it throws "'int java.io.InputStream.read(byte[])' on a null object reference" error.

Here is the java code:

public class MainActivity extends Activity
{
    TextView myLabel;
    EditText myTextbox;
    BluetoothAdapter mBluetoothAdapter;
    BluetoothSocket mmSocket;
    Button listen;
    BluetoothDevice mmDevice;
    OutputStream mmOutputStream;
    InputStream mmInputStream;
    Thread workerThread;
    byte[] readBuffer;
    int readBufferPosition;
    int counter;
    volatile boolean stopWorker;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button openButton = (Button)findViewById(R.id.open);
        Button sendButton = (Button)findViewById(R.id.send);
        listen=(Button)findViewById(R.id.listen);
        Button closeButton = (Button)findViewById(R.id.close);
        myLabel = (TextView)findViewById(R.id.label);
        myTextbox = (EditText)findViewById(R.id.entry);

        //Open Button
        openButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try
                {
                    findBT();
                    openBT();
                }
                catch (IOException ex) { }
            }
        });

        //Send Button
        sendButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try
                {
                    sendData();
                }
                catch (IOException ex) { }
            }
        });

        //Close button
        closeButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try
                {
                    closeBT();
                }
                catch (IOException ex) { }
            }
        });
        listen.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                beginListenForData();
            }
        });
    }

    void findBT()
    {
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(mBluetoothAdapter == null)
        {
            myLabel.setText("No bluetooth adapter available");
        }

        if(!mBluetoothAdapter.isEnabled())
        {
            Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBluetooth, 0);
        }

        Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
        if(pairedDevices.size() > 0)
        {
            for(BluetoothDevice device : pairedDevices)
            {
                if(device.getName().equals("Dual-SPP"))
                {
                    mmDevice = device;
                    break;
                }
            }
        }
        myLabel.setText("Bluetooth Device Found");
    }

    void openBT() throws IOException
    {
        UUID uuid = UUID.fromString("34341788-4dd0-11ec-a84d-575393abcb7e"); //Standard SerialPortService ID
        mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
        mmSocket.connect();
        mmOutputStream = mmSocket.getOutputStream();
        mmInputStream = mmSocket.getInputStream();

        beginListenForData();

        myLabel.setText("Bluetooth Opened");
    }

    public void beginListenForData()
    {
        final Handler handler = new Handler();
        final byte delimiter = 10; //This is the ASCII code for a newline character

        stopWorker = false;
        readBufferPosition = 0;
        readBuffer = new byte[1024];
        workerThread = new Thread(new Runnable()
        {
            public void run()
            {
                while(!Thread.currentThread().isInterrupted() && !stopWorker)
                {
                    try
                    {
                        int bytesAvailable;
                        bytesAvailable = mmInputStream.read();
                        if(bytesAvailable > 0)
                        {
                            byte[] packetBytes = new byte[bytesAvailable];
                            mmInputStream.read(packetBytes);
                            for(int i=0;i<bytesAvailable;i++)
                            {
                                byte b = packetBytes[i];
                                if(b == delimiter)
                                {
                                    byte[] encodedBytes = new byte[readBufferPosition];
                                    System.arraycopy(readBuffer, 0, encodedBytes, 0, encodedBytes.length);
                                    final String data = new String(encodedBytes, "US-ASCII");
                                    readBufferPosition = 0;

                                    handler.post(new Runnable()
                                    {
                                        public void run()
                                        {
                                            myLabel.setText(data);
                                        }
                                    });
                                }
                                else
                                {
                                    readBuffer[readBufferPosition++] = b;
                                }
                            }
                        }
                    }
                    catch (IOException ex)
                    {
                        stopWorker = true;
                    }
                }
            }
        });

        workerThread.start();
    }

    void sendData() throws IOException
    {
        String msg = myTextbox.getText().toString();
        msg += "\n";
        mmOutputStream.write(msg.getBytes());
        myLabel.setText("Data Sent");
    }

    void closeBT() throws IOException
    {
        stopWorker = true;
        mmOutputStream.close();
        mmInputStream.close();
        mmSocket.close();
        myLabel.setText("Bluetooth Closed");
    }
}

The error log:

FATAL EXCEPTION: Thread-2
    Process: com.example.spider_ecg, PID: 17829
    java.lang.NullPointerException: Attempt to invoke virtual method 'int java.io.InputStream.read()' on a null object reference

I don't know where is the issue starting from, And the serial port that am connecting sends data continuously without an start command, so I need to read the without a start. Is there any method to solve this issue or any other procedure.