Fix unit test

--HG--
branch : dev

src/Orchard/FileSystems/Dependencies/IDependenciesFolder.cs

@@ -1,8 +1,12 @@
 using System.Collections.Generic;
+using System.Linq;
 using Orchard.Caching;
 
 namespace Orchard.FileSystems.Dependencies {
     public class DependencyDescriptor {
+        public DependencyDescriptor() {
+            References = Enumerable.Empty<ReferenceDescriptor>();
+        }
         public string Name { get; set; }
         public string LoaderName { get; set; }
         public string VirtualPath { get; set; }