Using Android's AppCompat polyfill for Theme.Material in older Android versions

I've been working on getting our application to work with the ideas of Material Design, but also getting them to work in older versions of Android. Android's AppCompat library ships a theme, Theme.AppCompat.*, which is supposed to standardize things somewhat.

So currently, I have the usual in values-v21\styles.xml:

<style name="Theme.NW" parent="android:Theme.Material.Light.DarkActionBar">...</style>

I added the AppCompat package to the project. I finally figured out I needed to use the application styles instead of Android's ("@style/" instead of "android:"):

<style name="Theme.NW" parent="@style/Theme.AppCompat.Light.DarkActionBar">...</style>

Unfortunately, when I do this, I get a nasty exception:

Object reference not set to an instance of an object  at Xamarin.Forms.Platform.Android.Platform.UpdateActionBarBackgroundColor () [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.Platform.set_CurrentNavigationPage (Xamarin.Forms.NavigationPage value) [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.Platform.UpdateActionBar () [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.Platform.SetPage (Xamarin.Forms.Page newRoot) [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.FormsApplicationActivity.InternalSetPage (Xamarin.Forms.Page page) [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.FormsApplicationActivity.SetMainPage () [0x00000] in [filename unknown]:0 
  at Xamarin.Forms.Platform.Android.FormsApplicationActivity.LoadApplication (Xamarin.Forms.Application application) [0x00000] in [filename unknown]:0 
  at NW.Mobile.Droid.MainActivity.OnCreate (Android.OS.Bundle savedInstanceState) [0x001ac] in /Users/geoff/MyProject.Mobile/Android/MainActivity.cs:66 

Has anyone had success in doing this?