code: @TargetApi(Build.VERSION_CODES.O)
    public static void setDefaultChannelId(Context context, String channelId) {
      DefaultChannelId = channelId;
      if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.N_MR1) {
        // do nothing for Android versions before Ore
        return;
      }
  
      try {
        NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
        CharSequence name = context.getPackageName();
        String description = "PushNotification";
        int importance = NotificationManager.IMPORTANCE_DEFAULT;
        android.app.NotificationChannel channel = new android.app.NotificationChannel(channelId, name, importance);
        channel.setDescription(description);
        notificationManager.createNotificationChannel(channel);
      } catch (Exception ex) {
        LOGGER.w("failed to create NotificationChannel, then perhaps PushNotification doesn't work well on Android O and newer version.");
      }
    }
docs: Set default channel for Android Oreo or newer version
  Notice: it isn"t necessary to invoke this method for any Android version before Oreo.
  
  @param context   context
  @param channelId default channel id.