title: All notification removed while tapping on only one notification
body: <p>I have used Firebase messaging services and I have generated notifications. When I get multiple notification and when I tap on one notification then all other notifications get removed. I do not want to remove other untapped notifications. Here how I generate notification,</p>
  
  <pre><code>public class MyNotificationManager {
  
  private Context mCtx;
  private static  int notification_count=0;
  private static MyNotificationManager mInstance;
  public  static final String NOTIFICATION_CHANNEL_ID = "10001";
  private NotificationManager mNotificationManager;
  private NotificationCompat.Builder mBuilder;
  private MyNotificationManager(Context context) {
      mCtx = context;
  }
  public static synchronized MyNotificationManager getInstance(Context context) {
      if (mInstance == null) {
          mInstance = new MyNotificationManager(context);
      }
      return mInstance;
  }
  public void createNotification(String title, String message, int contentId)
  {
      /**Creates an explicit intent for an Activity in your app**/
      Intent resultIntent = new Intent(mCtx,HomeActivity.class);
      resultIntent.putExtra("contentId", "" + contentId);
      resultIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
  
      TaskStackBuilder mStackBuilder = TaskStackBuilder.create(mCtx);
      mStackBuilder.addNextIntent(resultIntent);
  
      PendingIntent resultPendingIntent =
              mStackBuilder.getPendingIntent(contentId, PendingIntent.FLAG_ONE_SHOT);
  
      mBuilder = new NotificationCompat.Builder(mCtx);
      mBuilder.setSmallIcon(R.mipmap.ic_launcher);
      mBuilder.setContentTitle(title)
              .setContentText(message)
              .setAutoCancel(true)
              .setSound(Settings.System.DEFAULT_NOTIFICATION_URI)
              .setContentIntent(resultPendingIntent);
  
      mNotificationManager = (NotificationManager) mCtx.getSystemService(Context.NOTIFICATION_SERVICE);
  
      if (android.os.Build.VERSION.SDK_INT &gt;= android.os.Build.VERSION_CODES.O)
      {
          int importance = NotificationManager.IMPORTANCE_DEFAULT;
          NotificationChannel notificationChannel = new NotificationChannel(NOTIFICATION_CHANNEL_ID,
                  "DEFAULT_CHANNEL", importance);
          notificationChannel.enableLights(true);
          notificationChannel.setLightColor(Color.RED);
          notificationChannel.enableVibration(true);
          notificationChannel.setVibrationPattern(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400});
          assert mNotificationManager != null;
          mBuilder.setChannelId(NOTIFICATION_CHANNEL_ID);
          mNotificationManager.createNotificationChannel(notificationChannel);
      }
  
      assert mNotificationManager != null;
      mNotificationManager.notify(notification_count++ /* Request Code */, mBuilder.build());
  }
  </code></pre>
  
  <p>}</p>