Fixes tree for single tree sections, fixes creating a user group so you can select default permissions

src/Umbraco.Web/Trees/ApplicationTreeController.cs

@@ -42,7 +42,7 @@ namespace Umbraco.Web.Trees
             //find all tree definitions that have the current application alias
             var appTrees = ApplicationContext.Current.Services.ApplicationTreeService.GetApplicationTrees(application, onlyInitialized).ToArray();
 
-            if (appTrees.Count() == 1 || string.IsNullOrEmpty(tree) == false )
+            if (string.IsNullOrEmpty(tree) == false || appTrees.Length == 1)
             {
                 var apptree = string.IsNullOrEmpty(tree) == false 
                     ? appTrees.SingleOrDefault(x => x.Alias == tree)
@@ -55,11 +55,12 @@ namespace Umbraco.Web.Trees
                     Constants.System.Root.ToString(CultureInfo.InvariantCulture),
                     queryStrings, 
                     application);
-
-                return result;
+
+                //this will be null if it cannot convert to ta single root section
+                if (result != null)
+                    return result;
             }
 
-
             var collection = new TreeNodeCollection();
             foreach (var apptree in appTrees)
             {
@@ -107,6 +108,7 @@ namespace Umbraco.Web.Trees
         /// <param name="configTree"></param>
         /// <param name="id"></param>
         /// <param name="queryStrings"></param>
+        /// <param name="application"></param>
         /// <returns></returns>
         private async Task<SectionRootNode> GetRootForSingleAppTree(ApplicationTree configTree, string id, FormDataCollection queryStrings, string application)
         {
@@ -121,6 +123,16 @@ namespace Umbraco.Web.Trees
                     //This should really never happen if we've successfully got the children above.
                     throw new InvalidOperationException("Could not create root node for tree " + configTree.Alias);
                 }
+
+                //if the root node has a route path, we cannot create a single root section because by specifying the route path this would
+                //override the dashboard route and that means there can be no dashboard for that section which is a breaking change.
+                if (rootNode.Result.RoutePath.IsNullOrWhiteSpace() == false 
+                    && rootNode.Result.RoutePath != "#" 
+                    && rootNode.Result.RoutePath != application)
+                {
+                    //null indicates this cannot be converted
+                    return null;
+                }
 
                 var sectionRoot = SectionRootNode.CreateSingleTreeSectionRoot(
                     rootId, 
@@ -128,6 +140,10 @@ namespace Umbraco.Web.Trees
                     rootNode.Result.MenuUrl, 
                     rootNode.Result.Name,
                     byControllerAttempt.Result);
+
+                //This can't be done currently because the root will default to routing to a dashboard and if we disable dashboards for a section
+                //that is really considered a breaking change. See above.
+                //sectionRoot.RoutePath = rootNode.Result.RoutePath;
 
                 foreach (var d in rootNode.Result.AdditionalData)
                 {