Fixing the issue #123

src/Microsoft.AspNet.Routing/OptionalRouteConstraint.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using Microsoft.AspNet.Http;
+
+namespace Microsoft.AspNet.Routing
+{
+    public class OptionalRouteConstraint : IRouteConstraint
+    {
+        public OptionalRouteConstraint([NotNull]IRouteConstraint innerConstraint)
+        {
+            InnerConstraint = innerConstraint;
+        }
+
+        public IRouteConstraint InnerConstraint { get; private set; }
+
+        public bool Match([NotNull]HttpContext httpContext,
+                          [NotNull]IRouter route,
+                          [NotNull]string routeKey,
+                          [NotNull]IDictionary<string, object> values,
+                          RouteDirection routeDirection)
+        {
+            object value;
+            if (values.TryGetValue(routeKey, out value) && value != null)
+            {
+                return InnerConstraint.Match(httpContext,
+                                             route,
+                                             routeKey,
+                                             values,
+                                             routeDirection);
+            }
+
+            return true;
+        }
+    }
+}