### Godot version

v4.0.beta.custom_build [eaf306e0b]

### System information

Windows 10

### Issue description

Selecting a `Window` node in the Editor's SceneTree results in the message
```
editor/editor_data.cpp:1058 - Parameter "p_node" is null.
```
and the Inspector shows empty content instead of the Window's properties.

I would expect, that clicking on a node in the SceneTree lets me edit the properties of the node.

Bisecting shows that this behavior got introduced in #71770

### Steps to reproduce

1. Create a Window node
2. Click on the Window node in the Editor's SceneTree

### Minimal reproduction project

N/A
edited_type = theme_type_list->get_item_text(p_index);
	_update_type_items();
}
void ThemeTypeEditor::_add_type_button_cbk() {
	add_type_mode = ADD_THEME_TYPE;
	add_type_dialog->set_title(TTR("Add Item Type"));
	add_type_dialog->set_ok_button_text(TTR("Add Type"));
	add_type_dialog->set_include_own_types(false);
	add_type_dialog->popup_centered(Size2(560, 420) * EDSCALE);
}
void ThemeTypeEditor::_add_default_type_items() {
	List<StringName> names;
	String default_type = edited_type;
	if (edited_theme->get_type_variation_base(edited_type) != StringName()) {
		default_type = edited_theme->get_type_variation_base(edited_type);
	}
	Ref<Theme> old_snapshot = edited_theme->duplicate();
	Ref<Theme> new_snapshot = edited_theme->duplicate();
	updating = true;
	{
		names.clear();
		ThemeDB::get_singleton()->get_default_theme()->get_icon_list(default_type, &names);
		for (const StringName &E : names) {
			if (!new_snapshot->has_icon(E, edited_type)) {