Make encoders registration optional (#140)

src/Microsoft.AspNetCore.StaticFiles/DirectoryBrowserMiddleware.cs

@@ -24,6 +24,17 @@ namespace Microsoft.AspNetCore.StaticFiles
         private readonly IDirectoryFormatter _formatter;
         private readonly IFileProvider _fileProvider;
 
+        /// <summary>
+        /// Creates a new instance of the SendFileMiddleware. Using <see cref="HtmlEncoder.Default"/> instance.
+        /// </summary>
+        /// <param name="next">The next middleware in the pipeline.</param>
+        /// <param name="hostingEnv">The <see cref="IHostingEnvironment"/> used by this middleware.</param>
+        /// <param name="options">The configuration for this middleware.</param>
+        public DirectoryBrowserMiddleware(RequestDelegate next, IHostingEnvironment hostingEnv, IOptions<DirectoryBrowserOptions> options) 
+            : this(next, hostingEnv, HtmlEncoder.Default, options)
+        {
+        }
+
         /// <summary>
         /// Creates a new instance of the SendFileMiddleware.
         /// </summary>

test/Microsoft.AspNetCore.StaticFiles.Tests/DirectoryBrowserMiddlewareTests.cs

@@ -19,6 +19,14 @@ namespace Microsoft.AspNetCore.StaticFiles
 {
     public class DirectoryBrowserMiddlewareTests
     {
+        [Fact]
+        public void WorksWithoutEncoderRegistered()
+        {
+            // No exception, uses HtmlEncoder.Default
+            StaticFilesTestServer.Create(
+                app => app.UseDirectoryBrowser());
+        }
+
         [Fact]
         public async Task NullArguments()
         {