Error message on no dispatcher middleware in endpoint middleware (#600)

src/Microsoft.AspNetCore.Routing/EndpointMiddleware.cs

@@ -32,6 +32,11 @@ namespace Microsoft.AspNetCore.Routing
         public async Task Invoke(HttpContext httpContext)
         {
             var feature = httpContext.Features.Get<IEndpointFeature>();
+            if (feature == null)
+            {
+                throw new InvalidOperationException("Unable to execute an endpoint because the dispatcher was not run. Ensure dispatcher middleware is registered.");
+            }
+
             if (feature.Invoker != null)
             {
                 Log.ExecutingEndpoint(_logger, feature.Endpoint);

test/Microsoft.AspNetCore.Routing.Tests/EndpointMiddlewareTest.cs

@@ -0,0 +1,48 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Logging.Testing;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Routing
+{
+    public class EndpointMiddlewareTest
+    {
+        [Fact]
+        public async Task Invoke_NoFeature_ThrowFriendlyErrorMessage()
+        {
+            // Arrange
+            var httpContext = new DefaultHttpContext();
+            httpContext.RequestServices = new ServiceProvider();
+
+            RequestDelegate next = (c) =>
+            {
+                return Task.FromResult<object>(null);
+            };
+
+            var middleware = new EndpointMiddleware(NullLogger<EndpointMiddleware>.Instance, next);
+
+            // Act
+            var invokeTask = middleware.Invoke(httpContext);
+
+            // Assert
+            var ex = await Assert.ThrowsAsync<InvalidOperationException>(async () => await invokeTask);
+
+            Assert.Equal("Unable to execute an endpoint because the dispatcher was not run. Ensure dispatcher middleware is registered.", ex.Message);
+        }
+
+        private class ServiceProvider : IServiceProvider
+        {
+            public object GetService(Type serviceType)
+            {
+                throw new NotImplementedException();
+            }
+        }
+    }
+}