Ensuring an app level middleware pipeline is registered

Author: fabiocav

src/WebJobs.Script.WebHost/Middleware/JobHostMiddleware/DefaultMiddlewarePipeline.cs

@@ -11,11 +11,15 @@ namespace Microsoft.Azure.WebJobs.Script.Middleware
 {
     internal class DefaultMiddlewarePipeline : IJobHostMiddlewarePipeline
     {
+        private static Lazy<IJobHostMiddlewarePipeline> _emptyPipeline = new Lazy<IJobHostMiddlewarePipeline>(() => new DefaultMiddlewarePipeline(Array.Empty<IJobHostHttpMiddleware>()));
+
         public DefaultMiddlewarePipeline(IEnumerable<IJobHostHttpMiddleware> middleware)
         {
             Pipeline = BuildPipeline(middleware);
         }
 
+        public static IJobHostMiddlewarePipeline Empty => _emptyPipeline.Value;
+
         public RequestDelegate Pipeline { get; }
 
         private RequestDelegate BuildPipeline(IEnumerable<IJobHostHttpMiddleware> middleware)

src/WebJobs.Script.WebHost/WebHostServiceCollectionExtensions.cs

@@ -7,6 +7,7 @@
 using Microsoft.Azure.WebJobs.Extensions.Http;
 using Microsoft.Azure.WebJobs.Script.Config;
 using Microsoft.Azure.WebJobs.Script.Diagnostics;
+using Microsoft.Azure.WebJobs.Script.Middleware;
 using Microsoft.Azure.WebJobs.Script.Rpc;
 using Microsoft.Azure.WebJobs.Script.WebHost.Configuration;
 using Microsoft.Azure.WebJobs.Script.WebHost.ContainerManagement;
@@ -127,6 +128,7 @@ public static void AddWebJobsScriptHost(this IServiceCollection services, IConfi
             services.ConfigureOptions<LanguageWorkerOptionsSetup>();
 
             services.TryAddSingleton<IDependencyValidator, DependencyValidator>();
+            services.TryAddSingleton<IJobHostMiddlewarePipeline>(s => DefaultMiddlewarePipeline.Empty);
         }
 
         private static void AddStandbyServices(this IServiceCollection services)