From b1e9c028286809c0f84130773654003ab0fc91dd Mon Sep 17 00:00:00 2001
From: "Luis v.d.Eltz" <luisvde@outlook.de>
Date: Wed, 11 Dec 2019 18:09:53 +0100
Subject: [PATCH 1/3] Adding TargetNullValue to BindingExtension

---
 .../MarkupExtensions/BindingExtension.cs                     | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs
index 1ceef5c824..3e1d85a913 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs
@@ -45,7 +45,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 Source = Source,
                 StringFormat = StringFormat,
                 RelativeSource = RelativeSource,
-                DefaultAnchor = new WeakReference(GetDefaultAnchor(descriptorContext))
+                DefaultAnchor = new WeakReference(GetDefaultAnchor(descriptorContext)),
+                TargetNullValue = TargetNullValue
             };
         }
 
@@ -83,5 +84,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         public string StringFormat { get; set; }
 
         public RelativeSource RelativeSource { get; set; }
+        
+        public object TargetNullValue { get; set; }
     }
 }

From e89d5af718f4e6614ecafb8f16a82ffbf4a8c571 Mon Sep 17 00:00:00 2001
From: "Luis v.d.Eltz" <luisvde@outlook.de>
Date: Thu, 12 Dec 2019 10:29:28 +0100
Subject: [PATCH 2/3] Adding unit test

---
 .../MarkupExtensions/BindingExtensionTests.cs | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
index c3bc649abb..fa7e7ead28 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
@@ -38,6 +38,27 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
                 Assert.Equal("foobar", textBlock.Text);
             }
         }
+        
+        [Fact]
+        public void BindingExtension_Binds_To_TargetNullValue()
+        {
+            using (StyledWindow())
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <TextBlock Name='textBlock' Text='{Binding Source={x:Null}, TargetNullValue='foobar'}'/>
+</Window>";
+
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var textBlock = window.FindControl<TextBlock>("textBlock");
+
+                window.Show();
+
+                Assert.Equal("foobar", textBlock.Text);
+            }
+        }
 
         private IDisposable StyledWindow(params (string, string)[] assets)
         {

From d88640b1eacfa6b79ff5c9a36abe093f432ac261 Mon Sep 17 00:00:00 2001
From: Luis von der Eltz <luis@gritworld.com>
Date: Thu, 12 Dec 2019 11:33:37 +0100
Subject: [PATCH 3/3] !B Fixing test

---
 .../MarkupExtensions/BindingExtensionTests.cs        | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
index fa7e7ead28..88c8034e52 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/BindingExtensionTests.cs
@@ -47,19 +47,29 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
                 var xaml = @"
 <Window xmlns='https://github.com/avaloniaui'
              xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
-    <TextBlock Name='textBlock' Text='{Binding Source={x:Null}, TargetNullValue='foobar'}'/>
+    <Window.Resources>
+        <x:String x:Key='text'>foobar</x:String>
+    </Window.Resources>
+
+    <TextBlock Name='textBlock' Text='{Binding Foo, TargetNullValue={StaticResource text}}'/>
 </Window>";
 
                 var loader = new AvaloniaXamlLoader();
                 var window = (Window)loader.Load(xaml);
                 var textBlock = window.FindControl<TextBlock>("textBlock");
 
+                window.DataContext = new FooBar();
                 window.Show();
 
                 Assert.Equal("foobar", textBlock.Text);
             }
         }
 
+        private class FooBar
+        {
+            public object Foo { get; } = null;
+        }
+
         private IDisposable StyledWindow(params (string, string)[] assets)
         {
             var services = TestServices.StyledWindow.With(