Steps to reproduce:

1. Open any Project
2. Right click in the Project Browser and select Create > UI Toolkit > Editor Window
3. In the UI Toolkit Editor Window Creator select "Choose Folder" and select any immutable Project folders (ProjectSettings, Library, Packages etc.)
4. Enter any string into the C# field and click the button "Confirm"

Actual results: The UI Toolkit Editor Window Creator Window becomes locked and has to be closed, Error is logged: "NullReferenceException: Object reference not set to an instance of an object
UnityEditor.UIElements.StyleSheets.URIHelpers.EncodeUri (System.String uri) (at <e19b8cc993aa46059ccba20cdf23f134>:0)
UnityEditor.UIElements.UIElementsEditorWindowCreator.CreateNewTemplatesFiles () (at <49948881918a4691bbfeb7755bb6fdb9>:0)
UnityEngine.UIElements.Clickable.Invoke (UnityEngine.UIElements.EventBase evt) (at <52787476209b4258babbe60e60b4d9e0>:0)"

Expected results: Immutable Project folders are counted among invalid Paths{}.{} The invalid path warning message is not descriptive enough and the warning is removed when selecting input fields.

Reproducible with versions: 6000.0.63f1, 6000.2.14f1, 6000.3.0f1, 6000.4.0a5, 6000.5.0a2

Tested on (OS): Windows 11