Why does getRootInActiveWindow() always returns null in Accessibility Event

Question

I have tried all the permutations and combinations of the AccessibilityServiceConfig.xml. Here is the code for AccecssibilityService and AccessibilityServiceConfig.xml.

Here is my code:

@Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
    
AccessibilityNodeInfo rootNode = getRootInActiveWindow();

}

@Override
    protected void onServiceConnected(){
        super.onServiceConnected();
         AccessibilityServiceInfo info = new AccessibilityServiceInfo();
        info.eventTypes                 = AccessibilityEvent.TYPES_ALL_MASK;
        info.feedbackType               = AccessibilityServiceInfo.FEEDBACK_SPOKEN;
        info.notificationTimeout        = 1000;
        info.flags                      = AccessibilityServiceInfo.FLAG_REPORT_VIEW_IDS;
        this.setServiceInfo(info);
        Log.e(TAG,"onServiceConnected: ");
    }

AccessibilityServiceConfig.xml:

<?xml version="1.0" encoding="utf-8"?>

    <accessibility-service xmlns:android="http://schemas.android.com/apk/res/android"
        android:accessibilityEventTypes="typeWindowsChanged|typeWindowContentChanged|typeViewScrolled"
        android:accessibilityFlags="flagReportViewIds|flagDefault|flagRetrieveInteractiveWindows|flagIncludeNotImportantViews"
        android:canPerformGestures="true"
        android:canRetrieveWindowContent="true"
        android:canRequestFilterKeyEvents="false"
        android:accessibilityFeedbackType="feedbackAllMask"
        android:notificationTimeout="1000"
        android:canRequestEnhancedWebAccessibility="true">
    </accessibility-service>

I have been using Samsung S21 Ultra for testing the app.