Few more NRT tweaks (#12323)

* Amended GetAll() on IDataTypeService to return an empty collection rather than null.

* Added a ClearSessionValue method to ISessionManager (given you can no longer set a value to null).

* Allow for null values in a StatefulNotification.

* Removed obsoletion of synchronous messages on TreeControllerBase.

* Fixed further CS8620 warnings in core project.

* Further fix to nullable warning.

* Aligned nullablility of retreiving tree nodes and menus, synchronously or asynchronously (such that we no longer can get null values, always empty collection objects).

src/Umbraco.Web.BackOffice/Controllers/DataTypeController.cs

@@ -424,8 +424,8 @@ namespace Umbraco.Cms.Web.BackOffice.Controllers
         [Authorize(Policy = AuthorizationPolicies.SectionAccessForDataTypeReading)]
         public IEnumerable<DataTypeBasic>? GetAll()
         {
-            return _dataTypeService?
-                     .GetAll()?
+            return _dataTypeService
+                     .GetAll()
                      .Select(_umbracoMapper.Map<IDataType, DataTypeBasic>).WhereNotNull().Where(x => x.IsSystemDataType == false);
         }
 
@@ -439,8 +439,8 @@ namespace Umbraco.Cms.Web.BackOffice.Controllers
         [Authorize(Policy = AuthorizationPolicies.SectionAccessForDataTypeReading)]
         public IDictionary<string, IEnumerable<DataTypeBasic>>? GetGroupedDataTypes()
         {
-            var dataTypes = _dataTypeService?
-                     .GetAll()?
+            var dataTypes = _dataTypeService
+                     .GetAll()
                      .Select(_umbracoMapper.Map<IDataType, DataTypeBasic>)
                      .ToArray();
 

src/Umbraco.Web.BackOffice/Trees/ContentBlueprintTreeController.cs

@@ -73,7 +73,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
 
             return root;
         }
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/ContentTreeControllerBase.cs

@@ -187,7 +187,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// </summary>
         protected abstract int[] UserStartNodes { get; }
 
-        protected virtual ActionResult<TreeNodeCollection?> PerformGetTreeNodes(string id, FormCollection queryStrings)
+        protected virtual ActionResult<TreeNodeCollection> PerformGetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 
@@ -345,7 +345,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// <remarks>
         /// This method is overwritten strictly to render the recycle bin, it should serve no other purpose
         /// </remarks>
-        protected sealed override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected sealed override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             //check if we're rendering the root
             if (id == Constants.System.RootString && UserStartNodes.Contains(Constants.System.Root))
@@ -384,7 +384,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
                         queryStrings.GetRequiredValue<string>("application") + TreeAlias.EnsureStartsWith('/') + "/recyclebin"));
                 }
 
-                return nodes;
+                return nodes ?? new TreeNodeCollection();
             }
 
             return GetTreeNodesInternal(id, queryStrings);
@@ -435,7 +435,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// <remarks>
         /// Currently this just checks if it is a container type, if it is we cannot render children. In the future this might check for other things.
         /// </remarks>
-        private ActionResult<TreeNodeCollection?> GetTreeNodesInternal(string id, FormCollection queryStrings)
+        private ActionResult<TreeNodeCollection> GetTreeNodesInternal(string id, FormCollection queryStrings)
         {
             var current = GetEntityFromId(id);
 

src/Umbraco.Web.BackOffice/Trees/ContentTypeTreeController.cs

@@ -58,7 +58,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             return root;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             if (!int.TryParse(id, NumberStyles.Integer, CultureInfo.InvariantCulture, out var intId))
             {

src/Umbraco.Web.BackOffice/Trees/DataTypeTreeController.cs

@@ -41,7 +41,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             _dataTypeService = dataTypeService;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             if (!int.TryParse(id, NumberStyles.Integer, CultureInfo.InvariantCulture, out var intId))
             {
@@ -71,7 +71,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             var systemListViewDataTypeIds = GetNonDeletableSystemListViewDataTypeIds();
 
             var children = _entityService.GetChildren(intId, UmbracoObjectTypes.DataType).ToArray();
-            var dataTypes = Enumerable.ToDictionary(_dataTypeService.GetAll(children.Select(c => c.Id).ToArray()) ?? Enumerable.Empty<IDataType>(), dt => dt.Id);
+            var dataTypes = Enumerable.ToDictionary(_dataTypeService.GetAll(children.Select(c => c.Id).ToArray()), dt => dt.Id);
 
             nodes.AddRange(
                 children

src/Umbraco.Web.BackOffice/Trees/DictionaryTreeController.cs

@@ -71,7 +71,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// We are allowing an arbitrary number of query strings to be passed in so that developers are able to persist custom data from the front-end
         /// to the back end to be used in the query for model data.
         /// </remarks>
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             if (!int.TryParse(id, NumberStyles.Integer, CultureInfo.InvariantCulture, out var intId))
             {

src/Umbraco.Web.BackOffice/Trees/FileSystemTreeController.cs

@@ -49,7 +49,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             treeNode.AdditionalData["jsClickCallback"] = "javascript:void(0);";
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var path = string.IsNullOrEmpty(id) == false && id != Constants.System.RootString
                 ? WebUtility.UrlDecode(id).TrimStart("/")

src/Umbraco.Web.BackOffice/Trees/LanguageTreeController.cs

@@ -17,24 +17,28 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
     [CoreTree]
     public class LanguageTreeController : TreeController
     {
+        private readonly IMenuItemCollectionFactory _menuItemCollectionFactory;
 
         public LanguageTreeController(
             ILocalizedTextService textService,
             UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection,
-            IEventAggregator eventAggregator)
+            IEventAggregator eventAggregator,
+            IMenuItemCollectionFactory menuItemCollectionFactory)
             : base(textService, umbracoApiControllerTypeCollection, eventAggregator)
         {
+            _menuItemCollectionFactory = menuItemCollectionFactory;
         }
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             //We don't have any child nodes & only use the root node to load a custom UI
             return new TreeNodeCollection();
         }
 
-        protected override ActionResult<MenuItemCollection>? GetMenuForNode(string id, FormCollection queryStrings)
+        protected override ActionResult<MenuItemCollection> GetMenuForNode(string id, FormCollection queryStrings)
         {
             //We don't have any menu item options (such as create/delete/reload) & only use the root node to load a custom UI
-            return null;
+            return _menuItemCollectionFactory.Create();
         }
 
         /// <summary>

src/Umbraco.Web.BackOffice/Trees/LogViewerTreeController.cs

@@ -17,24 +17,28 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
     [CoreTree]
     public class LogViewerTreeController : TreeController
     {
+        private readonly IMenuItemCollectionFactory _menuItemCollectionFactory;
+
         public LogViewerTreeController(
             ILocalizedTextService localizedTextService,
             UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection,
-            IEventAggregator eventAggregator)
+            IEventAggregator eventAggregator,
+            IMenuItemCollectionFactory menuItemCollectionFactory)
             : base(localizedTextService, umbracoApiControllerTypeCollection, eventAggregator)
         {
+            _menuItemCollectionFactory = menuItemCollectionFactory;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             //We don't have any child nodes & only use the root node to load a custom UI
             return new TreeNodeCollection();
         }
 
-        protected override ActionResult<MenuItemCollection>? GetMenuForNode(string id, FormCollection queryStrings)
+        protected override ActionResult<MenuItemCollection> GetMenuForNode(string id, FormCollection queryStrings)
         {
             //We don't have any menu item options (such as create/delete/reload) & only use the root node to load a custom UI
-            return null;
+            return _menuItemCollectionFactory.Create();
         }
 
         /// <summary>

src/Umbraco.Web.BackOffice/Trees/MacrosTreeController.cs

@@ -48,7 +48,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             return root;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/MediaTypeTreeController.cs

@@ -40,7 +40,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             _entityService = entityService;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             if (!int.TryParse(id, NumberStyles.Integer, CultureInfo.InvariantCulture, out var intId))
             {

src/Umbraco.Web.BackOffice/Trees/MemberTreeController.cs

@@ -104,7 +104,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             return node;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/MemberTypeAndGroupTreeControllerBase.cs

@@ -52,7 +52,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         {
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/PackagesTreeController.cs

@@ -56,7 +56,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         }
 
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             //full screen app without tree nodes
             return TreeNodeCollection.Empty;

src/Umbraco.Web.BackOffice/Trees/RelationTypeTreeController.cs

@@ -63,7 +63,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             return menu;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/StaticFilesTreeController.cs

@@ -16,18 +16,24 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
     public class StaticFilesTreeController : TreeController
     {
         private readonly IFileSystem _fileSystem;
+        private readonly IMenuItemCollectionFactory _menuItemCollectionFactory;
+
         private const string AppPlugins = "App_Plugins";
         private const string Webroot = "wwwroot";
 
-        public StaticFilesTreeController(ILocalizedTextService localizedTextService,
-            UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection, IEventAggregator eventAggregator,
-            IPhysicalFileSystem fileSystem) :
-            base(localizedTextService, umbracoApiControllerTypeCollection, eventAggregator)
+        public StaticFilesTreeController(
+            ILocalizedTextService localizedTextService,
+            UmbracoApiControllerTypeCollection umbracoApiControllerTypeCollection,
+            IEventAggregator eventAggregator,
+            IPhysicalFileSystem fileSystem,
+            IMenuItemCollectionFactory menuItemCollectionFactory)
+            : base(localizedTextService, umbracoApiControllerTypeCollection, eventAggregator)
         {
             _fileSystem = fileSystem;
+            _menuItemCollectionFactory = menuItemCollectionFactory;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var path = string.IsNullOrEmpty(id) == false && id != Constants.System.RootString
                 ? WebUtility.UrlDecode(id).TrimStart("/")
@@ -73,6 +79,6 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         }
 
         // We don't have any menu item options (such as create/delete/reload) & only use the root node to load a custom UI
-        protected override ActionResult<MenuItemCollection>? GetMenuForNode(string id, FormCollection queryStrings) => null;
+        protected override ActionResult<MenuItemCollection> GetMenuForNode(string id, FormCollection queryStrings) => _menuItemCollectionFactory.Create();
     }
 }

src/Umbraco.Web.BackOffice/Trees/TemplatesTreeController.cs

@@ -74,7 +74,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// We are allowing an arbitrary number of query strings to be pased in so that developers are able to persist custom data from the front-end
         /// to the back end to be used in the query for model data.
         /// </remarks>
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             var nodes = new TreeNodeCollection();
 

src/Umbraco.Web.BackOffice/Trees/TreeControllerBase.cs

@@ -47,8 +47,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// We are allowing an arbitrary number of query strings to be passed in so that developers are able to persist custom data from the front-end
         /// to the back end to be used in the query for model data.
         /// </remarks>
-        [Obsolete("See GetTreeNodesAsync")]
-        protected abstract ActionResult<TreeNodeCollection?> GetTreeNodes(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))]FormCollection queryStrings);
+        protected abstract ActionResult<TreeNodeCollection> GetTreeNodes(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))]FormCollection queryStrings);
 
         /// <summary>
         /// Returns the menu structure for the node
@@ -56,8 +55,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// <param name="id"></param>
         /// <param name="queryStrings"></param>
         /// <returns></returns>
-        [Obsolete("See GetMenuForNodeAsync")]
-        protected abstract ActionResult<MenuItemCollection>? GetMenuForNode(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))]FormCollection queryStrings);
+        protected abstract ActionResult<MenuItemCollection> GetMenuForNode(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))]FormCollection queryStrings);
 
         /// <summary>
         /// The method called to render the contents of the tree structure
@@ -71,7 +69,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// We are allowing an arbitrary number of query strings to be passed in so that developers are able to persist custom data from the front-end
         /// to the back end to be used in the query for model data.
         /// </remarks>
-        protected virtual async Task<ActionResult<TreeNodeCollection?>> GetTreeNodesAsync(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))] FormCollection queryStrings)
+        protected virtual async Task<ActionResult<TreeNodeCollection>> GetTreeNodesAsync(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))] FormCollection queryStrings)
         {
             return GetTreeNodes(id, queryStrings);
         }
@@ -85,7 +83,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
         /// <remarks>
         /// If overriden, GetMenuForNode will not be called
         /// </remarks>
-        protected virtual async Task<ActionResult<MenuItemCollection>?> GetMenuForNodeAsync(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))] FormCollection queryStrings)
+        protected virtual async Task<ActionResult<MenuItemCollection>> GetMenuForNodeAsync(string id, [ModelBinder(typeof(HttpQueryStringModelBinder))] FormCollection queryStrings)
         {
             return GetMenuForNode(id, queryStrings);
         }

src/Umbraco.Web.BackOffice/Trees/UserTreeController.cs

@@ -53,7 +53,7 @@ namespace Umbraco.Cms.Web.BackOffice.Trees
             return root;
         }
 
-        protected override ActionResult<TreeNodeCollection?> GetTreeNodes(string id, FormCollection queryStrings)
+        protected override ActionResult<TreeNodeCollection> GetTreeNodes(string id, FormCollection queryStrings)
         {
             //full screen app without tree nodes
             return TreeNodeCollection.Empty;