This REPL test page is based on the TreeView Filtering demo, but with added checkboxes.

1. Check an item.
2. Filter the TreeView data, so that the checked item is no longer present.
3. Try to check another item.
4. The TreeView will throw a NullReferenceException.

A possible workaround is to also filter (or clear) the collection that is bound to the CheckedItems parameter of the TreeView.