diff --git a/samples/Thinktecture.Runtime.Extensions.Samples/SmartEnums/SmartEnumDemos.cs b/samples/Thinktecture.Runtime.Extensions.Samples/SmartEnums/SmartEnumDemos.cs
index 56075559..dd7d626c 100644
--- a/samples/Thinktecture.Runtime.Extensions.Samples/SmartEnums/SmartEnumDemos.cs
+++ b/samples/Thinktecture.Runtime.Extensions.Samples/SmartEnums/SmartEnumDemos.cs
@@ -136,18 +136,18 @@ private static void DemoForNonValidatableEnum(ILogger logger)
 
       var returnValue = productType.Switch(ProductType.Groceries, static () => "Switch with Func<T>: Groceries",
                                            ProductType.Housewares, static () => "Switch with Func<T>: Housewares");
-      logger.Information(returnValue);
+      logger.Information("{ReturnValue}", returnValue);
 
       returnValue = productType.Switch(logger,
                                        ProductType.Groceries, static _ => "Switch with Func<T>: Groceries",
                                        ProductType.Housewares, static _ => "Switch with Func<T>: Housewares");
 
-      logger.Information(returnValue);
+      logger.Information("{ReturnValue}", returnValue);
 
       returnValue = productType.Map(ProductType.Groceries, "Map: Groceries",
                                     ProductType.Housewares, "Map: Housewares");
 
-      logger.Information(returnValue);
+      logger.Information("{ReturnValue}", returnValue);
 
       var parsed = ProductType.TryParse("Groceries", null, out var parsedProductType);
       logger.Information("Success: {Success} Parsed: {Parsed}", parsed, parsedProductType);
diff --git a/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/StructValueObjectMessagePackFormatter.cs b/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/StructValueObjectMessagePackFormatter.cs
index 618cc8c5..26a39e66 100644
--- a/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/StructValueObjectMessagePackFormatter.cs
+++ b/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/StructValueObjectMessagePackFormatter.cs
@@ -65,7 +65,7 @@ private static bool TryReadKey(
          return false;
       }
 
-      var formatter = options.Resolver.GetFormatterWithVerify<TKey>();
+      var formatter = options.Resolver.GetFormatterWithVerify<TKey?>();
       key = formatter.Deserialize(ref reader, options);
 
       return key is not null;
diff --git a/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/ValueObjectMessagePackFormatter.cs b/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/ValueObjectMessagePackFormatter.cs
index 9ddda59c..bcef5bfe 100644
--- a/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/ValueObjectMessagePackFormatter.cs
+++ b/src/Thinktecture.Runtime.Extensions.MessagePack/Formatters/ValueObjectMessagePackFormatter.cs
@@ -35,7 +35,7 @@ public void Serialize(ref MessagePackWriter writer, T? value, MessagePackSeriali
       if (reader.TryReadNil())
          return default;
 
-      var formatter = options.Resolver.GetFormatterWithVerify<TKey>();
+      var formatter = options.Resolver.GetFormatterWithVerify<TKey?>();
       var key = formatter.Deserialize(ref reader, options);
 
       if (key is null)
diff --git a/test/Thinktecture.Runtime.Extensions.Tests/ReadOnlyCollectionExtensions/ToReadOnlyCollection.cs b/test/Thinktecture.Runtime.Extensions.Tests/ReadOnlyCollectionExtensions/ToReadOnlyCollection.cs
index f89fefbd..9058c41f 100644
--- a/test/Thinktecture.Runtime.Extensions.Tests/ReadOnlyCollectionExtensions/ToReadOnlyCollection.cs
+++ b/test/Thinktecture.Runtime.Extensions.Tests/ReadOnlyCollectionExtensions/ToReadOnlyCollection.cs
@@ -3,6 +3,8 @@
 using System.Collections.Generic;
 using System.Linq;
 
+#nullable enable
+
 namespace Thinktecture.Runtime.Tests.ReadOnlyCollectionExtensions;
 
 public class ToReadOnlyCollection
@@ -10,14 +12,14 @@ public class ToReadOnlyCollection
    [Fact]
    public void Should_throw_if_items_is_null()
    {
-      0.Invoking(_ => ((IReadOnlyCollection<int>)null)!.ToReadOnlyCollection(i => _))
-       .Should().Throw<ArgumentNullException>();
+      FluentActions.Invoking(() => ((IReadOnlyCollection<int>)null!).ToReadOnlyCollection(i => i))
+                   .Should().Throw<ArgumentNullException>();
    }
 
    [Fact]
    public void Should_throw_if_count_is_negative()
    {
-      Array.Empty<int>().Invoking(e => e.ToReadOnlyCollection((Func<int, int>)null))
+      Array.Empty<int>().Invoking(e => e.ToReadOnlyCollection((Func<int, int>?)null!))
            .Should().Throw<ArgumentException>();
    }