Fix nullable

src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaRuntimeXamlLoader.cs

@@ -4,8 +4,6 @@ using System.Reflection;
 using System.Text;
 using Avalonia.Markup.Xaml.XamlIl;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml
 {
     public static class AvaloniaRuntimeXamlLoader

src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs

@@ -3,6 +3,8 @@ using System.Reflection;
 
 namespace Avalonia.Markup.Xaml;
 
+#nullable enable
+
 public class RuntimeXamlLoaderConfiguration
 {
     /// <summary>
@@ -13,7 +15,7 @@ public class RuntimeXamlLoaderConfiguration
     /// <summary>
     /// Default assembly for clr-namespace:.
     /// </summary>
-    public Assembly LocalAssembly { get; set; }
+    public Assembly? LocalAssembly { get; set; }
             
     /// <summary>
     /// The optional instance into which the XAML should be loaded.