Notification icon is not showing in android when we receive notification from firebase

Question

This is my Notification which i am receive notification from firebase.

this below code i have used to receive notification from firebase:

public class FirebaseMessageReceiver
        extends FirebaseMessagingService {
    Bitmap bitmap;

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        if (remoteMessage.getNotification().getImageUrl() != null) {
            String imageUri = remoteMessage.getNotification().getImageUrl().toString();
            bitmap = getBitmapfromUrl(imageUri);
            sendNotification(remoteMessage.getNotification().getTitle(), remoteMessage.getNotification().getBody(), bitmap);
        } else {
            sendNotification(remoteMessage.getNotification().getTitle(), remoteMessage.getNotification().getBody(), null);

        }
    }

    private void sendNotification(String messageTitle, String messageBody, Bitmap image) {
        NotificationManager mNotificationManager;

        NotificationCompat.Builder mBuilder =
                new NotificationCompat.Builder(this, "notify_001");
        Intent ii = new Intent(this, NotificationActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, ii, PendingIntent.FLAG_MUTABLE);
        NotificationCompat.BigTextStyle bigText = new NotificationCompat.BigTextStyle();
        bigText.bigText("");
        bigText.setBigContentTitle(messageTitle);
        mBuilder.setContentIntent(pendingIntent);
        mBuilder.setAutoCancel(true);
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            mBuilder.setSmallIcon(R.drawable.icon_transperent);
            mBuilder.setColor(getResources().getColor(R.color.full_transperent));
        } else {
            mBuilder.setSmallIcon(R.mipmap.ic_launcher_round);
        }
        if (image != null) {
            mBuilder.setLargeIcon(image);
        }
        mBuilder.setContentText(messageBody);
        mBuilder.setPriority(Notification.PRIORITY_MAX);
        mBuilder.setStyle(bigText);
        mNotificationManager =
                (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            String channelId = "Your_channel_id";
            NotificationChannel channel = new NotificationChannel(
                    channelId,
                    "Channel human readable title",
                    NotificationManager.IMPORTANCE_HIGH);
            mNotificationManager.createNotificationChannel(channel);
            mBuilder.setChannelId(channelId);
        }

        mNotificationManager.notify(0, mBuilder.build());
    }

    /*
     *To get a Bitmap image from the URL received
     * */
    public Bitmap getBitmapfromUrl(String imageUrl) {
        try {
            URL url = new URL(imageUrl);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setDoInput(true);
            connection.connect();
            InputStream input = connection.getInputStream();
            Bitmap bitmap = BitmapFactory.decodeStream(input);
            return bitmap;

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;

        }
    }
}

I don't know what i am doing mistake but i am getting notification from Firebase but i am unable to see icon its showing rounded black icon please help me how we can show icon in notification section when i receive notification .