Check in iOS if Navigation Bar Separator is hidden

I'm using Xamarin.Forms, and in iOS I made a custom render for PageRenderer where I can apply a gradient image to the NavigationBar.ShadowImage like below:

this.NavigationController.NavigationBar.ShadowImage = UIImage.FromFile("line_navigationbar.png");


In my project I have some Pages where the separator navigation bar is hidden like this:

On<iOS>().SetHideNavigationBarSeparator(true);


The problem is that my custom render applies the ShadowImage to all pages, including the ones I set to hide the separator. In my iOS custom render, how can I do like this:

if (!this.NavigationController.NavigationBar.isNavigationBarSeparatorHidden?) {
    this.NavigationController.NavigationBar.ShadowImage = UIImage.FromFile("line_navigationbar.png");
}

Is there a way to check in my iOS PageRenderer if the NavigationBarSeparator is set to hidden, so I apply the ShadowImage just to the correct pages?