diff --git a/ModernWpfPlayground.csproj b/ModernWpfPlayground.csproj
index ad58153..2ca7435 100644
--- a/ModernWpfPlayground.csproj
+++ b/ModernWpfPlayground.csproj
@@ -4,9 +4,14 @@
     <OutputType>WinExe</OutputType>
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <UseWPF>true</UseWPF>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.6">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
     <PackageReference Include="ModernWpfUI" Version="0.8.0" />
     <PackageReference Include="System.Drawing.Common" Version="4.7.0" />
   </ItemGroup>
diff --git a/MvvmStuff/BaseViewModel.cs b/MvvmStuff/BaseViewModel.cs
index c6f21e6..c22fb9f 100644
--- a/MvvmStuff/BaseViewModel.cs
+++ b/MvvmStuff/BaseViewModel.cs
@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.IO;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
 using System.Windows;
@@ -12,34 +11,34 @@ namespace ModernWpfPlayground.MvvmStuff
 {
     public abstract class BaseViewModel : INotifyPropertyChanged
     {
-        protected BaseViewModel()
-        {
-            _properties = GetType().GetProperties();
-        }
 
         private readonly Dictionary<string, object> _valueDict = new Dictionary<string, object>();
-        private readonly PropertyInfo[] _properties;
 
-        protected bool SetProperty<T>(T value, [CallerMemberName] string propertyName = null)
+        protected bool SetProperty<T>(T value, Action<T>? onChanged = null,
+            [CallerMemberName] string? propertyName = null)
         {
+            if(propertyName == null) throw new ArgumentNullException(nameof(propertyName));
             if (_valueDict.TryGetValue(propertyName, out var obj) && Equals(value, obj)) return false;
 
-            _valueDict[propertyName] = value;
+            _valueDict[propertyName] = value!;
             OnPropertyChanged(propertyName);
+            onChanged?.Invoke(value);
             return true;
         }
 
-        protected T GetProperty<T>(T defaultValue = default, [CallerMemberName] string propertyName = null)
+        protected T GetProperty<T>(T defaultValue = default, [CallerMemberName] string? propertyName = null)
         {
+            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
             return _valueDict.TryGetValue(propertyName, out var obj) ? (T) obj : defaultValue;
         }
 
-        public event PropertyChangedEventHandler PropertyChanged;
+        public event PropertyChangedEventHandler? PropertyChanged;
 
         [NotifyPropertyChangedInvocator]
         [PublicAPI]
-        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
+        protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
         {
+            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
         }
 
@@ -63,50 +62,14 @@ namespace ModernWpfPlayground.MvvmStuff
             }
         }
 
-        protected void LoadViewModel()
+        protected void MapDictionary(IEnumerable<(string, object?)> tuples)
         {
-            var openFileDialog = new OpenFileDialog {AddExtension = true, DefaultExt = "*.json"};
-            var result = openFileDialog.ShowDialog(Application.Current.MainWindow?.Owner);
-            if (result != true) return;
-            var contents = File.ReadAllText(openFileDialog.FileName);
-            var obj = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(contents);
-            foreach (var (key, value) in obj)
+            if (tuples == null) throw new ArgumentNullException(nameof(tuples));
+            foreach (var (key, value) in tuples)
             {
-                _valueDict[key] = CastToType(key, value);
+                _valueDict[key] = value!;
                 OnPropertyChanged(key);
             }
         }
-
-        private object CastToType(string key, JsonElement value)
-        {
-
-            var property = Array.Find(_properties, x => x.Name == key);
-            if (property.PropertyType == typeof(double))
-            {
-                return value.GetDouble();
-            }
-
-            if (property.PropertyType == typeof(bool))
-            {
-                return value.GetBoolean();
-            }
-
-            if (property.PropertyType == typeof(int))
-            {
-                return value.GetInt32();
-            }
-
-            if (property.PropertyType.IsEnum)
-            {
-                return Enum.ToObject(property.PropertyType, value.GetInt32());
-            }
-
-            if (property.PropertyType == typeof(string))
-            {
-                return value.GetString();
-            }
-
-            return default;
-        }
     }
 }
\ No newline at end of file
diff --git a/MvvmStuff/RelayCommand.cs b/MvvmStuff/RelayCommand.cs
index fd3f92c..71d5cc4 100644
--- a/MvvmStuff/RelayCommand.cs
+++ b/MvvmStuff/RelayCommand.cs
@@ -5,7 +5,7 @@ namespace ModernWpfPlayground.MvvmStuff
 {
     public class RelayCommand : ICommand
     {
-        private readonly Predicate<object> _canExecute;
+        private readonly Predicate<object>? _canExecute;
         private readonly Action<object> _execute;
 
         public RelayCommand(Action<object> execute)
diff --git a/PropertyPresenter2/ValueConverter.cs b/PropertyPresenter2/ValueConverter.cs
index 3a5c6bc..ec8ec80 100644
--- a/PropertyPresenter2/ValueConverter.cs
+++ b/PropertyPresenter2/ValueConverter.cs
@@ -16,7 +16,7 @@ namespace ModernWpfPlayground.PropertyPresenter2
     /// <summary>
     /// Makes an Bitmap from every Imageformat.
     /// </summary>
-    public class ObjectImageConverter : IValueConverter
+    public sealed class ObjectImageConverter : IValueConverter
     {
         object IValueConverter.Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
diff --git a/WindowViewModel.cs b/WindowViewModel.cs
index 1213f03..007e904 100644
--- a/WindowViewModel.cs
+++ b/WindowViewModel.cs
@@ -1,32 +1,47 @@
-using System.Threading.Tasks;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Reflection;
+using System.Text.Json;
+using System.Threading.Tasks;
 using System.Windows;
 using System.Windows.Input;
+using Microsoft.Win32;
 using ModernWpfPlayground.MvvmStuff;
 
 namespace ModernWpfPlayground
 {
     public class WindowViewModel : BaseViewModel
     {
+        private readonly PropertyInfo[] _properties;
+        private string? _path;
+
         public WindowViewModel()
         {
-            ShowDialogCommand = new RelayCommand(async x => await ShowDialogAsync());
+            ShowDialogCommand = new RelayCommand(async x => await ShowDialogAsync().ConfigureAwait(false));
             CloseCommand = new RelayCommand(x => Application.Current.Shutdown());
             OpenViewModelCommand = new RelayCommand(x => LoadViewModel());
             SaveViewModelCommand = new RelayCommand(x => SaveViewModel());
             ResetViewModelCommand = new RelayCommand(x => ResetViewModel());
+            _properties = GetType().GetProperties();
         }
 
         private async Task ShowDialogAsync()
         {
             var dialog = new ContentDialogExample {Message = WelcomeMessage};
-            var result = await dialog.ShowAsync();
+            var result = await dialog.ShowAsync().ConfigureAwait(false);
             WelcomeMessage = result.ToString();
         }
 
         public bool BooleanValue
         {
             get => GetProperty(true);
-            set => SetProperty(value);
+            set => SetProperty(value, BooleanValue_OnChanged);
+        }
+
+        private void BooleanValue_OnChanged(bool obj)
+        {
+            VisibilityEnumTest = obj ? Visibility.Visible : Visibility.Collapsed;
         }
 
         public Visibility VisibilityEnumTest
@@ -62,5 +77,61 @@ namespace ModernWpfPlayground
         public ICommand SaveViewModelCommand { get; }
 
         public ICommand ResetViewModelCommand { get; }
+
+        private void LoadViewModel()
+        {
+            var list = ReadFromJson();
+            MapDictionary(list);
+        }
+
+        private IEnumerable<(string, object?)> ReadFromJson()
+        {
+            var openFileDialog = new OpenFileDialog { AddExtension = true, DefaultExt = "*.json" };
+            var result = openFileDialog.ShowDialog(Application.Current.MainWindow?.Owner);
+            if (result != true) yield break;
+
+            var contents = File.ReadAllText(_path = openFileDialog.FileName);
+            var obj = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(contents);
+            foreach (var (key, value) in obj)
+            {
+                yield return (key, CastToType(key, value));
+            }
+        }
+
+        private object? CastToType(string key, JsonElement value)
+        {
+
+            var property = Array.Find(_properties, x => x.Name == key);
+            if (property == null)
+            {
+                return default;
+            }
+            if (property.PropertyType == typeof(double))
+            {
+                return value.GetDouble();
+            }
+
+            if (property.PropertyType == typeof(bool))
+            {
+                return value.GetBoolean();
+            }
+
+            if (property.PropertyType == typeof(int))
+            {
+                return value.GetInt32();
+            }
+
+            if (property.PropertyType.IsEnum)
+            {
+                return Enum.ToObject(property.PropertyType, value.GetInt32());
+            }
+
+            if (property.PropertyType == typeof(string))
+            {
+                return value.GetString();
+            }
+
+            return default;
+        }
     }
 }
\ No newline at end of file