Fix the last few warnings

Enables TreatWarningsAsErrors for all projects

Emby.Server.Implementations/Library/Resolvers/GenericFolderResolver.cs

@@ -0,0 +1,27 @@
+#nullable disable
+
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Library;
+
+namespace Emby.Server.Implementations.Library.Resolvers
+{
+    /// <summary>
+    /// Class FolderResolver.
+    /// </summary>
+    /// <typeparam name="TItemType">The type of the T item type.</typeparam>
+    public abstract class GenericFolderResolver<TItemType> : ItemResolver<TItemType>
+        where TItemType : Folder, new()
+    {
+        /// <summary>
+        /// Sets the initial item values.
+        /// </summary>
+        /// <param name="item">The item.</param>
+        /// <param name="args">The args.</param>
+        protected override void SetInitialItemValues(TItemType item, ItemResolveArgs args)
+        {
+            base.SetInitialItemValues(item, args);
+
+            item.IsRoot = args.Parent == null;
+        }
+    }
+}