Make an exception for root path (#15570)

src/Umbraco.Core/Services/FileServiceBase.cs

@@ -39,6 +39,15 @@ public abstract class FileServiceBase<TRepository, TEntity> : RepositoryService,
         return true;
     }
 
+    /// <summary>
+    /// Checks if a path is considered a root path.
+    /// </summary>
+    /// <param name="path">The path to check.</param>
+    /// <returns>True if the path is considered a root path.</returns>
+    protected virtual bool IsRootPath(string? path)
+    // We use "/" here instead of path separator because it's the virtual path used by backoffice, and not an actual FS path.
+        => string.IsNullOrWhiteSpace(path) || path == "/";
+
     /// <inheritdoc />
     public Task<TEntity?> GetAsync(string path)
     {

src/Umbraco.Core/Services/ScriptService.cs

@@ -105,13 +105,13 @@ public class ScriptService : FileServiceBase<IScriptRepository, IScript>, IScrip
             return Task.FromResult(ScriptOperationStatus.AlreadyExists);
         }
 
-        if (string.IsNullOrWhiteSpace(createModel.ParentPath) is false &&
-            Repository.FolderExists(createModel.ParentPath) is false)
+        if (IsRootPath(createModel.ParentPath) is false &&
+            Repository.FolderExists(createModel.ParentPath!) is false)
         {
             return Task.FromResult(ScriptOperationStatus.ParentNotFound);
         }
 
-        if(HasValidFileName(createModel.Name) is false)
+        if (HasValidFileName(createModel.Name) is false)
         {
             return Task.FromResult(ScriptOperationStatus.InvalidName);
         }

src/Umbraco.Core/Services/StylesheetService.cs

@@ -102,8 +102,8 @@ public class StylesheetService : FileServiceBase<IStylesheetRepository, IStylesh
             return StylesheetOperationStatus.AlreadyExists;
         }
 
-        if (string.IsNullOrWhiteSpace(createModel.ParentPath) is false
-            && Repository.FolderExists(createModel.ParentPath) is false)
+        if (IsRootPath(createModel.ParentPath) is false
+            && Repository.FolderExists(createModel.ParentPath!) is false)
         {
             return StylesheetOperationStatus.ParentNotFound;
         }