diff --git a/Directory.Packages.props b/Directory.Packages.props
index d6766a96..b2467d33 100644
--- a/Directory.Packages.props
+++ b/Directory.Packages.props
@@ -39,7 +39,7 @@
     <PackageVersion Include="Microsoft.Extensions.Diagnostics.Testing" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.Hosting" Version="$(MicrosoftExtensionsVersion)" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.8.1" />
-    <PackageVersion Include="NSubstitute" Version="5.3.0" />
+    <PackageVersion Include="NSubstitute" Version="6.0.0" />
     <PackageVersion Include="OpenTelemetry" Version="1.16.0" />
     <PackageVersion Include="OpenTelemetry.Exporter.InMemory" Version="1.16.0" />
     <PackageVersion Include="Reqnroll.xunit.v3" Version="3.3.4" />
diff --git a/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTests.cs b/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTests.cs
index b8e0131b..6f919f5e 100644
--- a/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTests.cs
+++ b/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTests.cs
@@ -449,7 +449,7 @@ public async Task EvaluateAsync_WithStrategySkippingProvider_DoesNotCallSkippedP
         this._mockStrategy.ShouldEvaluateThisProvider(Arg.Any<StrategyPerProviderContext<bool>>(), this._evaluationContext)
             .Returns(callInfo =>
             {
-                var context = callInfo.Arg<StrategyPerProviderContext<bool>>();
+                var context = callInfo.Arg<StrategyPerProviderContext<bool>>()!;
                 return context.ProviderName == Provider1Name; // Only evaluate provider1
             });
         this._mockStrategy.DetermineFinalResult(Arg.Any<StrategyEvaluationContext<bool>>(), TestFlagKey, defaultValue, this._evaluationContext, Arg.Any<List<ProviderResolutionResult<bool>>>())
diff --git a/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTrackingTests.cs b/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTrackingTests.cs
index 7f703ada..1830e925 100644
--- a/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTrackingTests.cs
+++ b/test/OpenFeature.Providers.MultiProvider.Tests/MultiProviderTrackingTests.cs
@@ -177,14 +177,14 @@ public async Task Track_WithCustomStrategy_RespectsStrategyDecision()
 
         // Only allow tracking with the first provider
         customStrategy.ShouldTrackWithThisProvider(
-            Arg.Is<StrategyPerProviderContext<object>>(ctx => ctx.ProviderName == Provider1Name),
+            Arg.Is<StrategyPerProviderContext<object>>(ctx => ctx!.ProviderName == Provider1Name),
             Arg.Any<EvaluationContext>(),
             Arg.Any<string>(),
             Arg.Any<TrackingEventDetails>()
         ).Returns(true);
 
         customStrategy.ShouldTrackWithThisProvider(
-            Arg.Is<StrategyPerProviderContext<object>>(ctx => ctx.ProviderName != Provider1Name),
+            Arg.Is<StrategyPerProviderContext<object>>(ctx => ctx!.ProviderName != Provider1Name),
             Arg.Any<EvaluationContext>(),
             Arg.Any<string>(),
             Arg.Any<TrackingEventDetails>()
diff --git a/test/OpenFeature.Providers.MultiProvider.Tests/ProviderExtensionsTests.cs b/test/OpenFeature.Providers.MultiProvider.Tests/ProviderExtensionsTests.cs
index dcf1dfe9..c66a2902 100644
--- a/test/OpenFeature.Providers.MultiProvider.Tests/ProviderExtensionsTests.cs
+++ b/test/OpenFeature.Providers.MultiProvider.Tests/ProviderExtensionsTests.cs
@@ -443,7 +443,7 @@ public async Task EvaluateAsync_WhenAfterHookThrowsException_LogsWarningButSucce
         this._mockLogger.Received(1).Log(
             LogLevel.Warning,
             Arg.Any<EventId>(),
-            Arg.Is<object>(v => v.ToString()!.Contains("Provider after/finally hook execution failed")),
+            Arg.Is<object>(v => v!.ToString()!.Contains("Provider after/finally hook execution failed")),
             Arg.Is<Exception>(ex => ex == hookException),
             Arg.Any<Func<object, Exception?, string>>());
     }
diff --git a/test/OpenFeature.Tests/OpenFeatureEventTests.cs b/test/OpenFeature.Tests/OpenFeatureEventTests.cs
index b32eb9bc..ff38e23a 100644
--- a/test/OpenFeature.Tests/OpenFeatureEventTests.cs
+++ b/test/OpenFeature.Tests/OpenFeatureEventTests.cs
@@ -51,7 +51,7 @@ public async Task Event_Executor_Should_Propagate_Events_ToGlobal_Handler()
 
         eventHandler.DidNotReceive().Invoke(newEventPayload);
 
-        eventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.Type == ProviderEventTypes.ProviderStale));
+        eventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.Type == ProviderEventTypes.ProviderStale));
     }
 
     [Fact]
@@ -79,28 +79,28 @@ await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
                 )));
 
         await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged
                 )));
 
         await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderError
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderError
                 )));
 
         await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderStale
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderStale
                 )));
     }
 
@@ -124,7 +124,7 @@ await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
                 )));
     }
 
@@ -148,7 +148,7 @@ await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady
                 )));
     }
 
@@ -174,7 +174,7 @@ await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderError
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderError
                 )));
     }
 
@@ -199,7 +199,7 @@ await Utils.AssertUntilAsync(_ => eventHandler
             .Received()
             .Invoke(
                 Arg.Is<ProviderEventPayload>(
-                    payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderStale
+                    payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderStale
                 )));
     }
 
@@ -227,10 +227,10 @@ public async Task API_Level_Event_Handlers_Should_Be_Exchangeable()
         await newTestProvider.SendEventAsync(ProviderEventTypes.ProviderConfigurationChanged, TestContext.Current.CancellationToken);
 
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received(2).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady))
+            _ => eventHandler.Received(2).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderReady))
         );
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received(2).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
+            _ => eventHandler.Received(2).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
         );
     }
 
@@ -254,7 +254,7 @@ public async Task API_Level_Event_Handlers_Should_Be_Removable()
         var newTestProvider = new TestProvider();
         await Api.Instance.SetProviderAsync(newTestProvider, TestContext.Current.CancellationToken);
 
-        eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name));
+        eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name));
     }
 
     [Fact]
@@ -280,10 +280,10 @@ public async Task API_Level_Event_Handlers_Should_Be_Executed_When_Other_Handler
         await Api.Instance.SetProviderAsync(testProvider, TestContext.Current.CancellationToken);
 
         await Utils.AssertUntilAsync(
-            _ => failingEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => failingEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
     }
 
@@ -306,7 +306,7 @@ public async Task Client_Level_Event_Handlers_Should_Be_Registered()
 
         myClient.AddHandler(ProviderEventTypes.ProviderReady, eventHandler);
 
-        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name));
+        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name));
     }
 
     [Fact]
@@ -336,10 +336,10 @@ public async Task Client_Level_Event_Handlers_Should_Be_Executed_When_Other_Hand
         await Api.Instance.SetProviderAsync(myClient.GetMetadata().Name!, testProvider, TestContext.Current.CancellationToken);
 
         await Utils.AssertUntilAsync(
-            _ => failingEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => failingEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
     }
 
@@ -369,11 +369,11 @@ public async Task Client_Level_Event_Handlers_Should_Be_Registered_To_Default_Pr
         myClientWithNoBoundProvider.AddHandler(ProviderEventTypes.ProviderReady, eventHandler);
         myClientWithBoundProvider.AddHandler(ProviderEventTypes.ProviderReady, clientEventHandler);
 
-        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == apiProvider.GetMetadata().Name));
-        eventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == clientProvider.GetMetadata().Name));
+        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == apiProvider.GetMetadata().Name));
+        eventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == clientProvider.GetMetadata().Name));
 
-        clientEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == clientProvider.GetMetadata().Name));
-        clientEventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == apiProvider.GetMetadata().Name));
+        clientEventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == clientProvider.GetMetadata().Name));
+        clientEventHandler.DidNotReceive().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == apiProvider.GetMetadata().Name));
     }
 
     [Fact]
@@ -403,7 +403,7 @@ public async Task Client_Level_Event_Handlers_Should_Be_Receive_Events_From_Name
         // verify that the client received the event from the default provider as there is no named provider registered yet
         await Utils.AssertUntilAsync(
             _ => clientEventHandler.Received(1)
-                .Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == defaultProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
+                .Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == defaultProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
         );
 
         // set the other provider specifically for the client
@@ -415,12 +415,12 @@ await Utils.AssertUntilAsync(
 
         // now the client should have received only the event from the named provider
         await Utils.AssertUntilAsync(
-            _ => clientEventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == clientProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
+            _ => clientEventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == clientProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
         );
         // for the default provider, the number of received events should stay unchanged
         await Utils.AssertUntilAsync(
             _ => clientEventHandler.Received(1)
-                .Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == defaultProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
+                .Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == defaultProvider.GetMetadata().Name && payload.Type == ProviderEventTypes.ProviderConfigurationChanged))
         );
     }
 
@@ -444,7 +444,7 @@ public async Task Client_Level_Event_Handlers_Should_Be_Informed_About_Ready_Sta
         // add the event handler after the provider has already transitioned into the ready state
         myClient.AddHandler(ProviderEventTypes.ProviderReady, eventHandler);
 
-        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name));
+        eventHandler.Received().Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name));
     }
 
     [Fact]
@@ -468,7 +468,7 @@ public async Task Client_Level_Event_Handlers_Should_Be_Removable()
 
         // wait for the first event to be received
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
 
         myClient.RemoveHandler(ProviderEventTypes.ProviderReady, eventHandler);
@@ -478,7 +478,7 @@ await Utils.AssertUntilAsync(
 
         // wait a bit and make sure we only have received the first event, but nothing after removing the event handler
         await Utils.AssertUntilAsync(
-            _ => eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload.ProviderName == testProvider.GetMetadata().Name))
+            _ => eventHandler.Received(1).Invoke(Arg.Is<ProviderEventPayload>(payload => payload!.ProviderName == testProvider.GetMetadata().Name))
         );
     }
 
diff --git a/test/OpenFeature.Tests/OpenFeatureHookTests.cs b/test/OpenFeature.Tests/OpenFeatureHookTests.cs
index 9acffa45..23a8e962 100644
--- a/test/OpenFeature.Tests/OpenFeatureHookTests.cs
+++ b/test/OpenFeature.Tests/OpenFeatureHookTests.cs
@@ -151,7 +151,7 @@ public async Task Evaluation_Context_Must_Be_Mutable_Before_Hook()
         await client.GetBooleanValueAsync("test", false, EvaluationContext.Empty, new FlagEvaluationOptions(ImmutableList.Create(hook1, hook2), ImmutableDictionary<string, object>.Empty), TestContext.Current.CancellationToken);
 
         _ = hook1.Received(1).BeforeAsync(Arg.Any<HookContext<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
-        _ = hook2.Received(1).BeforeAsync(Arg.Is<HookContext<bool>>(a => a.EvaluationContext.GetValue("test").AsString == "test"), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
+        _ = hook2.Received(1).BeforeAsync(Arg.Is<HookContext<bool>>(a => a!.EvaluationContext.GetValue("test").AsString == "test"), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
     }
 
     [Fact]
@@ -162,11 +162,11 @@ public async Task HookData_Must_Be_Mutable()
 
         hook.BeforeAsync(Arg.Any<HookContext<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(EvaluationContext.Empty).AndDoes(info =>
             {
-                info.Arg<HookContext<bool>>().Data.Set("test-a", true);
+                info.Arg<HookContext<bool>>()!.Data.Set("test-a", true);
             });
         hook.AfterAsync(Arg.Any<HookContext<bool>>(), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(new ValueTask()).AndDoes(info =>
         {
-            info.Arg<HookContext<bool>>().Data.Set("test-b", "test-value");
+            info.Arg<HookContext<bool>>()!.Data.Set("test-b", "test-value");
         });
 
         await Api.Instance.SetProviderAsync(new NoOpFeatureProvider(), TestContext.Current.CancellationToken);
@@ -175,10 +175,10 @@ public async Task HookData_Must_Be_Mutable()
         await client.GetBooleanValueAsync("test", false, EvaluationContext.Empty, new FlagEvaluationOptions(ImmutableList.Create(hook), ImmutableDictionary<string, object>.Empty), TestContext.Current.CancellationToken);
 
         _ = hook.Received(1).AfterAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("test-a") == true
+            (bool)hookContext!.Data.Get("test-a")
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
         _ = hook.Received(1).FinallyAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("test-a") == true && (string)hookContext.Data.Get("test-b") == "test-value"
+            (bool)hookContext!.Data.Get("test-a") && (string)hookContext.Data.Get("test-b") == "test-value"
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
     }
 
@@ -192,22 +192,22 @@ public async Task HookData_Must_Be_Unique_Per_Hook()
 
         hook1.BeforeAsync(Arg.Any<HookContext<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(EvaluationContext.Empty).AndDoes(info =>
             {
-                info.Arg<HookContext<bool>>().Data.Set("hook-1-value-a", true);
-                info.Arg<HookContext<bool>>().Data.Set("same", true);
+                info.Arg<HookContext<bool>>()!.Data.Set("hook-1-value-a", true);
+                info.Arg<HookContext<bool>>()!.Data.Set("same", true);
             });
         hook1.AfterAsync(Arg.Any<HookContext<bool>>(), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(new ValueTask()).AndDoes(info =>
         {
-            info.Arg<HookContext<bool>>().Data.Set("hook-1-value-b", "test-value-hook-1");
+            info.Arg<HookContext<bool>>()!.Data.Set("hook-1-value-b", "test-value-hook-1");
         });
 
         hook2.BeforeAsync(Arg.Any<HookContext<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(EvaluationContext.Empty).AndDoes(info =>
             {
-                info.Arg<HookContext<bool>>().Data.Set("hook-2-value-a", false);
-                info.Arg<HookContext<bool>>().Data.Set("same", false);
+                info.Arg<HookContext<bool>>()!.Data.Set("hook-2-value-a", false);
+                info.Arg<HookContext<bool>>()!.Data.Set("same", false);
             });
         hook2.AfterAsync(Arg.Any<HookContext<bool>>(), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken).Returns(new ValueTask()).AndDoes(info =>
         {
-            info.Arg<HookContext<bool>>().Data.Set("hook-2-value-b", "test-value-hook-2");
+            info.Arg<HookContext<bool>>()!.Data.Set("hook-2-value-b", "test-value-hook-2");
         });
 
         await Api.Instance.SetProviderAsync(new NoOpFeatureProvider(), TestContext.Current.CancellationToken);
@@ -217,19 +217,19 @@ public async Task HookData_Must_Be_Unique_Per_Hook()
                 ImmutableDictionary<string, object>.Empty), TestContext.Current.CancellationToken);
 
         _ = hook1.Received(1).AfterAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("hook-1-value-a") == true && (bool)hookContext.Data.Get("same") == true
+            (bool)hookContext!.Data.Get("hook-1-value-a") && (bool)hookContext.Data.Get("same")
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
         _ = hook1.Received(1).FinallyAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("hook-1-value-a") == true &&
+            (bool)hookContext!.Data.Get("hook-1-value-a") &&
             (bool)hookContext.Data.Get("same") == true &&
             (string)hookContext.Data.Get("hook-1-value-b") == "test-value-hook-1" && hookContext.Data.Count == 3
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
 
         _ = hook2.Received(1).AfterAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("hook-2-value-a") == false && (bool)hookContext.Data.Get("same") == false
+            !(bool)hookContext!.Data.Get("hook-2-value-a") && !(bool)hookContext.Data.Get("same")
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
         _ = hook2.Received(1).FinallyAsync(Arg.Is<HookContext<bool>>(hookContext =>
-            (bool)hookContext.Data.Get("hook-2-value-a") == false &&
+            !(bool)hookContext!.Data.Get("hook-2-value-a") &&
             (bool)hookContext.Data.Get("same") == false &&
             (string)hookContext.Data.Get("hook-2-value-b") == "test-value-hook-2" && hookContext.Data.Count == 3
         ), Arg.Any<FlagEvaluationDetails<bool>>(), Arg.Any<ImmutableDictionary<string, object>>(), TestContext.Current.CancellationToken);
@@ -308,7 +308,7 @@ public async Task Evaluation_Context_Must_Be_Merged_In_Correct_Order()
 
         // after proper merging, all properties should equal true
         _ = provider.Received(1).ResolveBooleanValueAsync(Arg.Any<string>(), Arg.Any<bool>(), Arg.Is<EvaluationContext>(y =>
-            (y.GetValue(propGlobal).AsBoolean ?? false)
+                    (y!.GetValue(propGlobal).AsBoolean ?? false)
             && (y.GetValue(propClient).AsBoolean ?? false)
             && (y.GetValue(propTransaction).AsBoolean ?? false)
             && (y.GetValue(propGlobalToOverwrite).AsBoolean ?? false)