Update TaskResultConverter Test to handle UnsetValue case

Author: Rosuavio

UnitTests/UnitTests.UWP/Converters/Test_TaskResultConverter.cs

@@ -8,6 +8,7 @@
 using Microsoft.Toolkit.Uwp.UI.Converters;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Microsoft.VisualStudio.TestTools.UnitTesting.AppContainer;
+using Windows.UI.Xaml;
 
 namespace UnitTests.Converters
 {
@@ -70,12 +71,19 @@ public void Test_TaskResultConverter_Instance_String()
 
         [TestCategory("Converters")]
         [UITestMethod]
-        public void Test_TaskResultConverter_Instance_Null()
+        public void Test_TaskResultConverter_Instance_UnsetValue()
         {
             var converter = new TaskResultConverter();
 
-            Assert.AreEqual(null, converter.Convert(null, null, null, null));
-            Assert.AreEqual(null, converter.Convert("Hello world", null, null, null));
+            Assert.AreEqual(DependencyProperty.UnsetValue, converter.Convert(null, null, null, null));
+            Assert.AreEqual(DependencyProperty.UnsetValue, converter.Convert("Hello world", null, null, null));
+         }
+
+        [TestCategory("Converters")]
+        [UITestMethod]
+        public void Test_TaskResultConverter_Instance_Null()
+        {
+            var converter = new TaskResultConverter();
 
             var cts = new CancellationTokenSource();