From a10c13626ccc50daa71fc1d777fa30a645ee6f65 Mon Sep 17 00:00:00 2001
From: Kevin Pilch <me@pilchie.com>
Date: Sat, 5 May 2018 15:22:08 -0700
Subject: [PATCH 1/2] Remove compilers package

---
 SampleTestAssembly/SampleTestAssembly.csproj   | 7 -------
 SampleTestAssembly/packages.config             | 1 -
 xunit.runner.data/xunit.runner.data.csproj     | 5 -----
 xunit.runner.worker/packages.config            | 1 -
 xunit.runner.worker/xunit.runner.worker.csproj | 7 -------
 xunit.runner.wpf/packages.config               | 1 -
 xunit.runner.wpf/xunit.runner.wpf.csproj       | 2 --
 7 files changed, 24 deletions(-)

diff --git a/SampleTestAssembly/SampleTestAssembly.csproj b/SampleTestAssembly/SampleTestAssembly.csproj
index ed3c179..88b95d7 100644
--- a/SampleTestAssembly/SampleTestAssembly.csproj
+++ b/SampleTestAssembly/SampleTestAssembly.csproj
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props" Condition="Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" />
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
@@ -66,12 +65,6 @@
     <None Include="packages.config" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
-  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
-    <PropertyGroup>
-      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
-    </PropertyGroup>
-    <Error Condition="!Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props'))" />
-  </Target>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">
diff --git a/SampleTestAssembly/packages.config b/SampleTestAssembly/packages.config
index bd8805d..44a585a 100644
--- a/SampleTestAssembly/packages.config
+++ b/SampleTestAssembly/packages.config
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="Microsoft.Net.Compilers" version="2.2.0" targetFramework="net452" developmentDependency="true" />
   <package id="xunit" version="2.1.0" targetFramework="net452" />
   <package id="xunit.abstractions" version="2.0.0" targetFramework="net452" />
   <package id="xunit.assert" version="2.1.0" targetFramework="net452" />
diff --git a/xunit.runner.data/xunit.runner.data.csproj b/xunit.runner.data/xunit.runner.data.csproj
index f82cf93..ddeabe8 100644
--- a/xunit.runner.data/xunit.runner.data.csproj
+++ b/xunit.runner.data/xunit.runner.data.csproj
@@ -48,11 +48,6 @@
     <Compile Include="TestDataKind.cs" />
     <Compile Include="TestResultData.cs" />
   </ItemGroup>
-  <ItemGroup>
-    <PackageReference Include="Microsoft.Net.Compilers">
-      <Version>2.2.0</Version>
-    </PackageReference>
-  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
diff --git a/xunit.runner.worker/packages.config b/xunit.runner.worker/packages.config
index 6afb8ce..f3e206d 100644
--- a/xunit.runner.worker/packages.config
+++ b/xunit.runner.worker/packages.config
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="Microsoft.Net.Compilers" version="2.2.0" targetFramework="net46" developmentDependency="true" />
   <package id="xunit.abstractions" version="2.0.0" targetFramework="net452" />
   <package id="xunit.runner.utility" version="2.1.0" targetFramework="net46" />
 </packages>
\ No newline at end of file
diff --git a/xunit.runner.worker/xunit.runner.worker.csproj b/xunit.runner.worker/xunit.runner.worker.csproj
index 33fcbe1..5f90231 100644
--- a/xunit.runner.worker/xunit.runner.worker.csproj
+++ b/xunit.runner.worker/xunit.runner.worker.csproj
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props" Condition="Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" />
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
@@ -77,12 +76,6 @@
     </ProjectReference>
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
-  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
-    <PropertyGroup>
-      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
-    </PropertyGroup>
-    <Error Condition="!Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props'))" />
-  </Target>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">
diff --git a/xunit.runner.wpf/packages.config b/xunit.runner.wpf/packages.config
index 70abc07..eeaf669 100644
--- a/xunit.runner.wpf/packages.config
+++ b/xunit.runner.wpf/packages.config
@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
   <package id="CommonServiceLocator" version="1.3" targetFramework="net452" />
-  <package id="Microsoft.Net.Compilers" version="2.2.0" targetFramework="net46" developmentDependency="true" />
   <package id="MvvmLight" version="5.3.0.0" targetFramework="net46" />
   <package id="MvvmLightLibs" version="5.3.0.0" targetFramework="net46" />
   <package id="NuGet.CommandLine" version="2.8.3" targetFramework="net46" />
diff --git a/xunit.runner.wpf/xunit.runner.wpf.csproj b/xunit.runner.wpf/xunit.runner.wpf.csproj
index d902b82..551bc09 100644
--- a/xunit.runner.wpf/xunit.runner.wpf.csproj
+++ b/xunit.runner.wpf/xunit.runner.wpf.csproj
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props" Condition="Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" />
   <Import Project="..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.props" Condition="Exists('..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.props')" />
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup>
@@ -216,7 +215,6 @@
     </PropertyGroup>
     <Error Condition="!Exists('..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.props'))" />
     <Error Condition="!Exists('..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.targets'))" />
-    <Error Condition="!Exists('..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Net.Compilers.2.2.0\build\Microsoft.Net.Compilers.props'))" />
   </Target>
   <Import Project="..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.targets" Condition="Exists('..\packages\Tvl.NuGet.BuildTasks.1.0.0-alpha002\build\Tvl.NuGet.BuildTasks.targets')" />
 </Project>
\ No newline at end of file

From a96ce278d28a54c51cf15e6f7425575131f9be43 Mon Sep 17 00:00:00 2001
From: Kevin Pilch <me@pilchie.com>
Date: Sat, 5 May 2018 16:20:05 -0700
Subject: [PATCH 2/2] Fix nullability warnings

---
 xunit.runner.data/ClientReader.cs             |  2 +-
 xunit.runner.wpf/CommandBindings.cs           |  8 ++---
 .../Converters/TestStateConverter.cs          |  2 +-
 xunit.runner.wpf/FilteredCollectionView.cs    |  8 ++++-
 .../Impl/RemoteTestUtil.BackgroundRunner.cs   | 11 ++++---
 .../Impl/RemoteTestUtil.Connection.cs         |  4 +--
 xunit.runner.wpf/Impl/RemoteTestUtil.cs       |  2 +-
 xunit.runner.wpf/Impl/TestAssemblyWatcher.cs  |  2 +-
 xunit.runner.wpf/MainWindow.xaml.cs           |  3 ++
 xunit.runner.wpf/Persistence/Storage.cs       |  2 +-
 .../ViewModel/AssemblyAndConfigFile.cs        |  4 +--
 xunit.runner.wpf/ViewModel/MainViewModel.cs   | 30 +++++++++++--------
 xunit.runner.wpf/ViewModel/TraitViewModel.cs  |  4 +--
 13 files changed, 46 insertions(+), 36 deletions(-)

diff --git a/xunit.runner.data/ClientReader.cs b/xunit.runner.data/ClientReader.cs
index 30678a5..51b7e36 100644
--- a/xunit.runner.data/ClientReader.cs
+++ b/xunit.runner.data/ClientReader.cs
@@ -7,7 +7,7 @@ public sealed class ClientReader : IDisposable
     {
         private readonly BinaryReader _reader;
         private bool _closed;
-        private Exception _exception;
+        private Exception? _exception;
 
         public bool IsConnected => !_closed;
 
diff --git a/xunit.runner.wpf/CommandBindings.cs b/xunit.runner.wpf/CommandBindings.cs
index 42048e9..087e22d 100644
--- a/xunit.runner.wpf/CommandBindings.cs
+++ b/xunit.runner.wpf/CommandBindings.cs
@@ -16,16 +16,14 @@ public static void SetRegistration(UIElement element, CommandBindingCollection v
             }
         }
 
-        public static CommandBindingCollection GetRegistration(UIElement element)
+        public static CommandBindingCollection? GetRegistration(UIElement element)
             => (element != null ? (CommandBindingCollection)element.GetValue(Registration) : null);
 
         private static void OnRegistrationChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
         {
-            UIElement element = sender as UIElement;
-            if (element != null)
+            if (sender is UIElement element)
             {
-                CommandBindingCollection bindings = e.NewValue as CommandBindingCollection;
-                if (bindings != null)
+                if (e.NewValue is CommandBindingCollection bindings)
                 {
                     element.CommandBindings.AddRange(bindings);
                 }
diff --git a/xunit.runner.wpf/Converters/TestStateConverter.cs b/xunit.runner.wpf/Converters/TestStateConverter.cs
index 46f1cc3..2341e5b 100644
--- a/xunit.runner.wpf/Converters/TestStateConverter.cs
+++ b/xunit.runner.wpf/Converters/TestStateConverter.cs
@@ -33,7 +33,7 @@ private static BitmapImage LoadResourceImage(string resourceName)
             return image;
         }
 
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        public object? Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
             var state = (TestState)value;
             if (targetType == typeof(Brush))
diff --git a/xunit.runner.wpf/FilteredCollectionView.cs b/xunit.runner.wpf/FilteredCollectionView.cs
index a4e2f15..4f194a9 100644
--- a/xunit.runner.wpf/FilteredCollectionView.cs
+++ b/xunit.runner.wpf/FilteredCollectionView.cs
@@ -283,7 +283,13 @@ void IList.RemoveAt(int index)
 
         object IList.this[int index]
         {
-            get { return this[index]; }
+            get
+            {
+                // Can't figure out how to not get a warning here.
+#pragma warning disable CS8603
+                return this[index];
+#pragma warning restore
+            }
             set { throw new NotSupportedException(); }
         }
 
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil.BackgroundRunner.cs b/xunit.runner.wpf/Impl/RemoteTestUtil.BackgroundRunner.cs
index 6e4907a..70cf7c1 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil.BackgroundRunner.cs
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil.BackgroundRunner.cs
@@ -55,13 +55,13 @@ private void GoOnBackground()
         /// <typeparam name="T"></typeparam>
         private sealed class BackgroundReader<T> where T : class
         {
-            private readonly ConcurrentQueue<T> _queue;
+            private readonly ConcurrentQueue<T?> _queue;
             private readonly ClientReader _reader;
             private readonly Func<ClientReader, T> _readValue;
 
             internal ClientReader Reader => _reader;
 
-            internal BackgroundReader(ConcurrentQueue<T> queue, ClientReader reader, Func<ClientReader, T> readValue)
+            internal BackgroundReader(ConcurrentQueue<T?> queue, ClientReader reader, Func<ClientReader, T> readValue)
             {
                 _queue = queue;
                 _reader = reader;
@@ -111,7 +111,7 @@ private sealed class BackgroundProducer<T> where T : class
             private const int MaxResultPerTick = 1000;
 
             private readonly Connection _connection;
-            private readonly ConcurrentQueue<T> _queue;
+            private readonly ConcurrentQueue<T?> _queue;
             private readonly DispatcherTimer _timer;
             private readonly Action<List<T>> _callback;
             private readonly int _maxPerTick;
@@ -122,7 +122,7 @@ private sealed class BackgroundProducer<T> where T : class
             internal BackgroundProducer(
                 Connection connection, 
                 Dispatcher dispatcher, 
-                ConcurrentQueue<T> queue,
+                ConcurrentQueue<T?> queue,
                 Action<List<T>> callback,
                 int maxResultPerTick = MaxResultPerTick,
                 TimeSpan? interval = null)
@@ -144,8 +144,7 @@ private void OnTimerTick(object sender, EventArgs e)
                 var i = 0;
                 var list = new List<T>();
                 var isDone = false;
-                T value;
-                while (i < _maxPerTick && _queue.TryDequeue(out value))
+                while (i < _maxPerTick && _queue.TryDequeue(out T? value))
                 {
                     if (value == null)
                     {
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil.Connection.cs b/xunit.runner.wpf/Impl/RemoteTestUtil.Connection.cs
index 7b93849..3a728e7 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil.Connection.cs
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil.Connection.cs
@@ -8,10 +8,10 @@ internal sealed partial class RemoteTestUtil : ITestUtil
     {
         private sealed class Connection : IDisposable
         {
-            private NamedPipeClientStream _stream;
+            private NamedPipeClientStream? _stream;
             private ClientReader _reader;
 
-            internal NamedPipeClientStream Stream => _stream;
+            internal NamedPipeClientStream Stream => _stream ?? throw new ObjectDisposedException(nameof(Connection));
 
             internal ClientReader Reader => _reader;
 
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil.cs b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
index 0c97f1c..5b86087 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil.cs
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
@@ -123,7 +123,7 @@ private async Task RunCore(string actionName, string assemblyPath, ImmutableArra
         private async Task ProcessResultsCore<T>(Connection connection, Func<ClientReader, T> readValue, Action<List<T>> callback, CancellationToken cancellationToken)
             where T : class
         {
-            var queue = new ConcurrentQueue<T>();
+            var queue = new ConcurrentQueue<T?>();
             var backgroundReader = new BackgroundReader<T>(queue, new ClientReader(connection.Stream), readValue);
             var backgroundProducer = new BackgroundProducer<T>(connection, _dispatcher, queue, callback);
 
diff --git a/xunit.runner.wpf/Impl/TestAssemblyWatcher.cs b/xunit.runner.wpf/Impl/TestAssemblyWatcher.cs
index 612e2eb..66379fa 100644
--- a/xunit.runner.wpf/Impl/TestAssemblyWatcher.cs
+++ b/xunit.runner.wpf/Impl/TestAssemblyWatcher.cs
@@ -14,7 +14,7 @@ internal sealed class TestAssemblyWatcher : ITestAssemblyWatcher
         private readonly IDictionary<string, FileSystemWatcher> watchedAssemblies = new Dictionary<string, FileSystemWatcher>();
         private readonly Dispatcher dispatcher;
         private bool isEnabled = false;
-        private ReloadDebouncer debouncer;
+        private ReloadDebouncer? debouncer;
 
         public TestAssemblyWatcher(Dispatcher dispatcher)
         {
diff --git a/xunit.runner.wpf/MainWindow.xaml.cs b/xunit.runner.wpf/MainWindow.xaml.cs
index d46e4e1..2317a5a 100644
--- a/xunit.runner.wpf/MainWindow.xaml.cs
+++ b/xunit.runner.wpf/MainWindow.xaml.cs
@@ -11,12 +11,15 @@ public partial class MainWindow : Window
     {
         public static Window Instance { get; private set; }
 
+        // WPF generates fields that are marked as non-nullable, but not definitely initialized.
+#pragma warning disable CS8618
         public MainWindow()
         {
             Instance = this;
 
             InitializeComponent();
         }
+#pragma warning restore
 
         protected override void OnSourceInitialized(EventArgs e)
         {
diff --git a/xunit.runner.wpf/Persistence/Storage.cs b/xunit.runner.wpf/Persistence/Storage.cs
index dd79b19..d4092cb 100644
--- a/xunit.runner.wpf/Persistence/Storage.cs
+++ b/xunit.runner.wpf/Persistence/Storage.cs
@@ -16,7 +16,7 @@ internal static partial class Storage
 
         private static IsolatedStorageFile GetStorageFile() => IsolatedStorageFile.GetUserStoreForDomain();
 
-        public static XmlTextReader OpenXmlFile(string fileName)
+        public static XmlTextReader? OpenXmlFile(string fileName)
         {
             var storage = GetStorageFile();
             if (!storage.FileExists(fileName))
diff --git a/xunit.runner.wpf/ViewModel/AssemblyAndConfigFile.cs b/xunit.runner.wpf/ViewModel/AssemblyAndConfigFile.cs
index 5085ac1..2fbe8b2 100644
--- a/xunit.runner.wpf/ViewModel/AssemblyAndConfigFile.cs
+++ b/xunit.runner.wpf/ViewModel/AssemblyAndConfigFile.cs
@@ -5,9 +5,9 @@ namespace Xunit.Runner.Wpf.ViewModel
     public class AssemblyAndConfigFile
     {
         public string AssemblyFileName { get; }
-        public string ConfigFileName { get; }
+        public string? ConfigFileName { get; }
 
-        public AssemblyAndConfigFile(string assemblyFileName, string configFileName)
+        public AssemblyAndConfigFile(string assemblyFileName, string? configFileName)
         {
             this.AssemblyFileName = Path.GetFullPath(assemblyFileName);
             if (configFileName != null)
diff --git a/xunit.runner.wpf/ViewModel/MainViewModel.cs b/xunit.runner.wpf/ViewModel/MainViewModel.cs
index 6da0ad2..7960e88 100644
--- a/xunit.runner.wpf/ViewModel/MainViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/MainViewModel.cs
@@ -33,7 +33,7 @@ public class MainViewModel : ViewModelBase
 
         private CancellationTokenSource filterCancellationTokenSource = new CancellationTokenSource();
 
-        private CancellationTokenSource cancellationTokenSource;
+        private CancellationTokenSource? cancellationTokenSource;
         private bool isBusy;
         private SearchQuery searchQuery = new SearchQuery();
         private bool autoReloadAssemblies;
@@ -54,7 +54,7 @@ public bool AutoReloadAssemblies
 
         public ObservableCollection<RecentAssemblyViewModel> RecentAssemblies { get; } = new ObservableCollection<RecentAssemblyViewModel>();
 
-        private ImmutableList<TestCaseViewModel> testsToRun;
+        private ImmutableList<TestCaseViewModel>? testsToRun;
 
         public ICommand ExitCommand { get; }
         public ICommand WindowLoadedCommand { get; }
@@ -63,7 +63,6 @@ public bool AutoReloadAssemblies
         public RelayCommand RunSelectedCommand { get; }
         public RelayCommand CancelCommand { get; }
         public ICommand TraitCheckedChangedCommand { get; }
-        public ICommand TraitSelectionChangedCommand { get; }
         public ICommand TraitsClearCommand { get; }
         public ICommand AssemblyReloadCommand { get; }
         public ICommand AssemblyReloadAllCommand { get; }
@@ -215,8 +214,8 @@ public List<TestAssemblyViewModel> SelectedAssemblies
             get { return Assemblies.Where(x => x.IsSelected).ToList(); }
         }
 
-        private string testCasesCaption;
-        public string TestCasesCaption
+        private string? testCasesCaption;
+        public string? TestCasesCaption
         {
             get { return testCasesCaption; }
             private set { Set(ref testCasesCaption, value); }
@@ -234,8 +233,8 @@ public int TestsCompleted
             }
         }
 
-        private TestCaseViewModel selectedTest;
-        public TestCaseViewModel SelectedTestCase
+        private TestCaseViewModel? selectedTest;
+        public TestCaseViewModel? SelectedTestCase
         {
             get { return selectedTest; }
 
@@ -401,7 +400,7 @@ await this.ExecuteTestSessionOperation(() =>
                     var taskList = new List<Task>();
                     foreach (var assembly in assemblies)
                     {
-                        taskList.Add(this.testUtil.Discover(assembly.AssemblyFileName, this.OnTestsDiscovered, this.cancellationTokenSource.Token));
+                        taskList.Add(this.testUtil.Discover(assembly.AssemblyFileName, this.OnTestsDiscovered, CancellationToken));
 
                         var assemblyViewModel = new TestAssemblyViewModel(assembly);
 
@@ -427,6 +426,11 @@ await this.ExecuteTestSessionOperation(() =>
             }
         }
 
+        private CancellationToken CancellationToken
+            => cancellationTokenSource == null
+                ? CancellationToken.None
+                : cancellationTokenSource.Token;
+
         public bool ReloadAssemblies(IEnumerable<string> assemblies)
         {
             if (IsBusy)
@@ -454,7 +458,7 @@ await ExecuteTestSessionOperation(() =>
                         var assemblyFileName = assemblyViewModel.FileName;
                         RemoveAssemblyTestCases(assemblyFileName);
 
-                        taskList.Add(this.testUtil.Discover(assemblyFileName, OnTestsDiscovered, cancellationTokenSource.Token));
+                        taskList.Add(this.testUtil.Discover(assemblyFileName, OnTestsDiscovered, CancellationToken));
                     }
 
                     return taskList;
@@ -549,7 +553,7 @@ private IEnumerable<AssemblyAndConfigFile> ParseCommandLine(IEnumerable<string>
                 var assemblyFileName = enumerable.First();
                 enumerable = enumerable.Skip(1);
 
-                var configFileName = (string)null;
+                var configFileName = (string?)null;
                 if (IsConfigFile(enumerable.FirstOrDefault()))
                 {
                     configFileName = enumerable.First();
@@ -630,7 +634,7 @@ private List<Task> RunTests(ImmutableList<TestCaseViewModel> tests)
                 Task task;
                 if (runAll)
                 {
-                    task = this.testUtil.RunAll(assemblyFileName, OnTestStateChange, this.cancellationTokenSource.Token);
+                    task = this.testUtil.RunAll(assemblyFileName, OnTestStateChange, CancellationToken);
                 }
                 else
                 {
@@ -644,7 +648,7 @@ private List<Task> RunTests(ImmutableList<TestCaseViewModel> tests)
                         }
                     }
 
-                    task = this.testUtil.RunSpecific(assemblyFileName, builder.ToImmutable(), OnTestStateChange, this.cancellationTokenSource.Token);
+                    task = this.testUtil.RunSpecific(assemblyFileName, builder.ToImmutable(), OnTestStateChange, CancellationToken);
                 }
 
                 testSessionList.Add(task);
@@ -778,7 +782,7 @@ private bool CanExecuteCancel()
         private void OnExecuteCancel()
         {
             Debug.Assert(CanExecuteCancel());
-            this.cancellationTokenSource.Cancel();
+            cancellationTokenSource?.Cancel();
         }
 
         private void OnExecuteTraitCheckedChanged(TraitViewModel trait)
diff --git a/xunit.runner.wpf/ViewModel/TraitViewModel.cs b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
index a12334b..5788a56 100644
--- a/xunit.runner.wpf/ViewModel/TraitViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/TraitViewModel.cs
@@ -7,7 +7,7 @@ namespace Xunit.Runner.Wpf.ViewModel
 {
     public partial class TraitViewModel : ViewModelBase
     {
-        private readonly TraitViewModel _parent;
+        private readonly TraitViewModel? _parent;
         private bool? _isChecked;
         private bool _isExpanded;
         private string _text;
@@ -19,7 +19,7 @@ public TraitViewModel(string text)
         {
         }
 
-        private TraitViewModel(TraitViewModel parent, string text)
+        private TraitViewModel(TraitViewModel? parent, string text)
         {
             this._parent = parent;
             this._isChecked = false;