Use standard ASP.NET null guard

Author: dustinbyrne

src/PostHog.AspNetCore/Tracing/PostHogRequestContextMiddlewareExtensions.cs

@@ -1,6 +1,4 @@
 using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Features;
 
 namespace PostHog;
 
@@ -19,36 +17,11 @@ public static IApplicationBuilder UsePostHogRequestContext(
         this IApplicationBuilder app,
         Action<PostHogRequestContextOptions>? configure = null)
     {
-        if (app is null)
-        {
-            return new NoOpApplicationBuilder();
-        }
+        ArgumentNullException.ThrowIfNull(app);
 
         var options = new PostHogRequestContextOptions();
         configure?.Invoke(options);
         return app.UseMiddleware<PostHogRequestContextMiddleware>(options);
     }
 
-    sealed class NoOpApplicationBuilder : IApplicationBuilder
-    {
-        readonly IFeatureCollection _serverFeatures = new FeatureCollection();
-        readonly IDictionary<string, object?> _properties = new Dictionary<string, object?>();
-
-        public IServiceProvider ApplicationServices { get; set; } = new NoOpServiceProvider();
-
-        public IFeatureCollection ServerFeatures => _serverFeatures;
-
-        public IDictionary<string, object?> Properties => _properties;
-
-        public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware) => this;
-
-        public IApplicationBuilder New() => new NoOpApplicationBuilder();
-
-        public RequestDelegate Build() => _ => Task.CompletedTask;
-    }
-
-    sealed class NoOpServiceProvider : IServiceProvider
-    {
-        public object? GetService(Type serviceType) => null;
-    }
 }

tests/UnitTests.AspNetCore/PostHogRequestContextMiddlewareTests.cs

@@ -21,12 +21,10 @@ public async Task NullHttpContextDoesNotThrow()
     }
 
     [Fact]
-    public async Task NullApplicationBuilderReturnsNoOpBuilder()
+    public void NullApplicationBuilderThrowsArgumentNullException()
     {
-        var app = PostHogRequestContextMiddlewareExtensions.UsePostHogRequestContext(null!);
-
-        Assert.NotNull(app);
-        await app.Build()(new DefaultHttpContext());
+        Assert.Throws<ArgumentNullException>(
+            () => PostHogRequestContextMiddlewareExtensions.UsePostHogRequestContext(null!));
     }
 
     [Fact]