Removed redundant null checks and tested logging

src/Microsoft.AspNet.Mvc.Core/FileResult.cs

@@ -71,7 +71,7 @@ namespace Microsoft.AspNet.Mvc
             }
 
             var loggerFactory = context.HttpContext.RequestServices.GetRequiredService<ILoggerFactory>();
-            var logger = loggerFactory?.CreateLogger<FileResult>();
+            var logger = loggerFactory.CreateLogger<FileResult>();
 
             var response = context.HttpContext.Response;
             response.ContentType = ContentType.ToString();

test/Microsoft.AspNet.Mvc.Core.Test/FileResultTest.cs

@@ -1,6 +1,7 @@
 // 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.IO;
 using System.Net.Mime;
 using System.Threading.Tasks;
@@ -120,6 +121,39 @@ namespace Microsoft.AspNet.Mvc
             Assert.Equal("attachment; filename=filename.ext; filename*=UTF-8''filename.ext", httpContext.Response.Headers["Content-Disposition"]);
         }
 
+        [Fact]
+        public async Task ExecuteResultAsync_ThrowsException_IfCannotResolveLoggerFactory()
+        {
+            // Arrange
+            var httpContext = new DefaultHttpContext();
+            httpContext.RequestServices = new ServiceCollection().BuildServiceProvider();
+            var actionContext = CreateActionContext(httpContext);
+            var result = new EmptyFileResult("application/my-type");
+
+            // Act & Assert
+            await Assert.ThrowsAsync<InvalidOperationException>(() => result.ExecuteResultAsync(actionContext));
+        }
+
+        [Fact]
+        public async Task ExecuteResultAsync_LogsInformation_IfCanResolveLoggerFactory()
+        {
+            // Arrange
+            var httpContext = new DefaultHttpContext();
+            var services = new ServiceCollection();
+            var loggerSink = new TestSink();
+            services.AddSingleton<ILoggerFactory>(new TestLoggerFactory(loggerSink, true));
+            httpContext.RequestServices = services.BuildServiceProvider();
+
+            var actionContext = CreateActionContext(httpContext);
+            var result = new EmptyFileResult("application/my-type");
+
+            // Act
+            await result.ExecuteResultAsync(actionContext);
+
+            // Assert
+            Assert.Equal(1, loggerSink.Writes.Count);
+        }
+
         public static TheoryData<string, string> ContentDispositionData
         {
             get