Showing high importance notifications on different android OS versions

AndroidNotificationHelper

    public void showNotification(String message, PendingIntent pendingIntent) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            createNotificationChannel();
        }

        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, "")
                .setSmallIcon(R.drawable.ic_icon)
                .setColor(ContextCompat.getColor(getApplicationContext(), R.color.color_primary_blue))
                .setContentTitle(getString(R.string.app_name))
                .setContentText(message)
                .setAutoCancel(true)
                .setChannelId("channel_id");

        if (pendingIntent != null) {
            mBuilder.setContentIntent(pendingIntent);
        }

        mBuilder.setDefaults(NotificationCompat.DEFAULT_ALL);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            mBuilder.setPriority(NotificationManager.IMPORTANCE_HIGH);
        } else {
            mBuilder.setPriority(Notification.PRIORITY_HIGH);
        }
        NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(999, mBuilder.build());
    }

    @RequiresApi(api = Build.VERSION_CODES.O)
    private void createNotificationChannel() {
        String name = getString(R.string.app_name);
        String description = getString(R.string.notifcation_description);
        int importance = NotificationManager.IMPORTANCE_HIGH;
        NotificationChannel channel = new NotificationChannel("channel_id"), name, importance);
        channel.setDescription(description);
        channel.enableVibration(true);

        NotificationManager notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        if (notificationManager != null) {
            notificationManager.createNotificationChannel(channel);
        }
    }