NullReferenceException / Java.Lang.NullPointerException

I get the following java interop exception:

Java.Lang.NullPointerException
  Message=Attempt to invoke virtual method 'void android.view.ViewGroup.getLocationOnScreen(int[])' on a null object reference

Renderer source code:

public FormsBlurViewRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<FormsBlurView> e)
        {
            base.OnElementChanged(e);

            if (Control != null)
            {
                return;
            }
            var context = Context;
            var activity = context as Activity;

            var rootView = (ViewGroup)activity?.Window?.DecorView?.FindViewById(Android.Resource.Id.Content);

            var blurView = new BlurView(context);

            blurView.SetupWith(rootView)
                .SetBlurRadius(3F)
                .SetOverlayColor(Resource.Color.foreground_material_light)
                .SetBlurAlgorithm(new RenderScriptBlur(context))
                .SetBlurRadius(10f);

            SetNativeControl(blurView);
        }

Implementation source code:

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyNamespace.MyClass" xmlns:local="clr-namespace:MyNamespace;assembly=MySolution">
    <ContentView.GestureRecognizers>
        <TapGestureRecognizer Tapped="TapGestureRecognizer_OnTapped" />
    </ContentView.GestureRecognizers>
    <ContentView.Content>
        <local:FormsBlurView>
            <RelativeLayout HeightRequest="150" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" BackgroundColor="Red">
                <Image x:Name="PreviewImage" Aspect="AspectFill" HorizontalOptions="CenterAndExpand" />
                <BoxView x:Name="FavoriteView" HeightRequest="150" HorizontalOptions="CenterAndExpand" />

                <Label x:Name="TitleLabel" HeightRequest="150" TextColor="#FFFFFF" FontSize="24" HorizontalTextAlignment="End" VerticalTextAlignment="End" HorizontalOptions="FillAndExpand" VerticalOptions="EndAndExpand" Margin="10, 0" />
            </RelativeLayout>
        </local:FormsBlurView>
    </ContentView.Content>
</ContentView>

wcoder / Xamarin.BlurView

NullReferenceException / Java.Lang.NullPointerException #8