Android bluetooth cannot enter BroadcastReceiver

I am trying to search for bluetooth device in Android. I am following the tutorial in this page. I test by printing log but it can only print 1 but not 2. It means it cannot enter the BroadcastReceiver. I tried to move the receiver inside registerReceiver with calling function but it does not work. May I ask why?

public class ScanList extends AppCompatActivity {

BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
BroadcastReceiver mReceiver;
int REQUEST_ENABLE_BT = 1;
ArrayAdapter<String> mArrayAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_scan_list);


    if (mBluetoothAdapter != null) {
        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            if (ContextCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(
                        this,
                        new String[]{Manifest.permission.BLUETOOTH_CONNECT}, REQUEST_ENABLE_BT
                );
            }
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }
    }

    IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
    registerReceiver(receiver, filter);
    mBluetoothAdapter.startDiscovery();
    Log.i("devi", "1");   // can only print this line
}

// Create a BroadcastReceiver for ACTION_FOUND.
private BroadcastReceiver receiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        Log.i("devi", "2");
        String action = intent.getAction();

        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // Discovery has found a device. Get the BluetoothDevice
            // object and its info from the Intent.
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            if (ActivityCompat.checkSelfPermission(ScanList.this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(
                        ScanList.this,
                        new String[]{Manifest.permission.BLUETOOTH_CONNECT}, REQUEST_ENABLE_BT
                );
            }
            String deviceName = device.getName();
            String deviceHardwareAddress = device.getAddress(); // MAC address
            Log.i("devi", deviceName);
            Log.i("devi", deviceHardwareAddress);


            Intent reintent = new Intent(ScanList.this, MainActivity.class);
            Bundle extras = new Bundle();
            extras.putString("name",deviceName);
            extras.putString("address",deviceHardwareAddress);
            reintent.putExtras(extras);
            startActivity(reintent);
            finish();
        }
    }
};

@Override
protected void onDestroy() {
    super.onDestroy();
    unregisterReceiver(receiver);
}
}

Edit

I can get device now by adding

if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(
                            MainActivity.this,
                            new String[]{Manifest.permission.BLUETOOTH_CONNECT}, 1001
                );

     }

in front of mBluetoothAdapter.startDiscovery(); and String deviceName = device.getName();. However, it is very unstable that clicking scan is not a must to enter BroadcastReceiver. Also, it crash when enter BroadcastReceiver. It said

Bluetooth keeps stopping

Bluetooth is my app name. How can I solve this?

Edit2

I have solved it. The problem is that not every device has a name. If it scans a device without name and shows in logcat, it gives null and crash. To solve it just add if statement and check whether getName is null.

The problem is that not every device has a name. If it scans a device without name and shows in logcat, it gives null and crash. To solve it just add if statement and check whether getName is null.