Bluetooth server socket android

Question

I am using Bluetooth in my app to connect with a thermal printer. First I check if Bluetooth is enabled or not and everything is fine. But I am facing a problem when I close Bluetooth while in app or not. My app crashes with a null pointer exception which is not handled in the BluetoothService class.

Also, I have notice that even if I am not in my app and I close the Bluetooth it calls my app and shows me a toast message from my code.

dose anyone faced this problem?

here is the null pointer exception from bluetooth server socket

03-03 17:13:27.576 9916-10431/co.lvlz.skiplino.provider E/AndroidRuntime: FATAL EXCEPTION: AcceptThread Process: co.lvlz.skiplino.provider, PID: 9916
java.lang.NullPointerException: Attempt to invoke virtual method 'android.bluetooth.BluetoothSocket 
android.bluetooth.BluetoothServerSocket.accept()' on a null object reference at com.zj.btsdk.BluetoothService$AcceptThread.run(BluetoothService.java:316)

here Bluetooth is handled and how I destroy the activity

private final Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BluetoothService.MESSAGE_STATE_CHANGE:
                    switch (msg.arg1) {
                        case BluetoothService.STATE_CONNECTED:   
                            Toast.makeText(getApplicationContext(), "Connect successful",
                                    Toast.LENGTH_SHORT).show();

                            break;
                        case BluetoothService.STATE_CONNECTING:  
                            Log.d("��������","��������.....");
                            break;
                        case BluetoothService.STATE_LISTEN:    
                        case BluetoothService.STATE_NONE:

                       Toast.makeText(getApplicationContext(), "bluetooth is closed",
                                    Toast.LENGTH_SHORT).show();

                            Log.d("None", "stateNone");
                            MainActivity.this.finish();


                            break;
                    }


                    break;

                case BluetoothService.MESSAGE_CONNECTION_LOST:
                    Log.d("None", "connection lost to device");

                Toast.makeText(getApplicationContext(),"Connetion was lost to device",
                            Toast.LENGTH_SHORT).show();


                    break;
                case BluetoothService.MESSAGE_UNABLE_CONNECT:
                    Toast.makeText(getApplicationContext(), "Unable to connect device",
                            Toast.LENGTH_SHORT).show();

                    break;
            }
        }

    };




protected void onDestroy() {
        super.onDestroy();
        if (mService != null)
        {

            Log.d("None", "nullMe");
            activitydestroyed=true;
            mService.stop();


        }

        else {
            Log.d("None", "nullMe2");
            mService = null;

        }
    }