### 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
import_items_filter->clear();
	selected_items.clear();
	total_selected_colors_label->hide();
	total_selected_constants_label->hide();
	total_selected_fonts_label->hide();
	total_selected_font_sizes_label->hide();
	total_selected_icons_label->hide();
	total_selected_styleboxes_label->hide();
	_update_items_tree();
}
bool ThemeItemImportTree::has_selected_items() const {
	return (selected_items.size() > 0);
}
void ThemeItemImportTree::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_ENTER_TREE:
		case NOTIFICATION_THEME_CHANGED: {
			select_icons_warning_icon->set_texture(get_theme_icon(SNAME("StatusWarning"), SNAME("EditorIcons")));
			select_icons_warning->add_theme_color_override("font_color", get_theme_color(SNAME("disabled_font_color"), SNAME("Editor")));
			import_items_filter->set_right_icon(get_theme_icon(SNAME("Search"), SNAME("EditorIcons")));
			
			import_collapse_types_button->set_icon(get_theme_icon(SNAME("CollapseTree"), SNAME("EditorIcons")));
			import_expand_types_button->set_icon(get_theme_icon(SNAME("ExpandTree"), SNAME("EditorIcons")));
			import_select_all_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			import_select_full_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			import_deselect_all_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			
			select_colors_icon->set_texture(get_theme_icon(SNAME("Color"), SNAME("EditorIcons")));