update extension methods

src/Libraries/Microsoft.Extensions.Http.Diagnostics/Http/HttpDependencyMetadataResolver.cs

@@ -63,7 +63,7 @@
     {
         try
         {
-            if (requestMessage?.RequestUri == null)
+            if (requestMessage.RequestUri == null)
             {
                 return null;
             }

src/Libraries/Microsoft.Extensions.Http.Diagnostics/Http/HttpDiagnosticsServiceCollectionExtensions.cs

@@ -23,10 +23,9 @@ public static class HttpDiagnosticsServiceCollectionExtensions
     public static IServiceCollection AddDownstreamDependencyMetadata(this IServiceCollection services, IDownstreamDependencyMetadata downstreamDependencyMetadata)
     {
         _ = Throw.IfNull(services);
-        _ = Throw.IfNull(downstreamDependencyMetadata);
-
-        services.TryAddEnumerable(ServiceDescriptor.Singleton<IDownstreamDependencyMetadata>(downstreamDependencyMetadata));
         services.TryAddSingleton<HttpDependencyMetadataResolver, DefaultHttpDependencyMetadataResolver>();
+        _ = services.AddSingleton(downstreamDependencyMetadata);
+
         return services;
     }
 
@@ -40,8 +39,8 @@ public static IServiceCollection AddDownstreamDependencyMetadata(this IServiceCo
         where T : class, IDownstreamDependencyMetadata
     {
         _ = Throw.IfNull(services);
-        services.TryAddEnumerable(ServiceDescriptor.Singleton<IDownstreamDependencyMetadata, T>());
         services.TryAddSingleton<HttpDependencyMetadataResolver, DefaultHttpDependencyMetadataResolver>();
+        _ = services.AddSingleton<IDownstreamDependencyMetadata, T>();
         return services;
     }