### 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
arr.push_back(idx + 1);
			arr.push_back(selected_items.size());
			ProgressDialog::get_singleton()->task_step("import_theme_items", TTR("Importing items {n}/{n}").format(arr, "{n}"), idx);
		}
		ItemCheckedState cs = E.value;
		ThemeItem ti = E.key;
		if (cs == SELECT_IMPORT_DEFINITION || cs == SELECT_IMPORT_FULL) {
			Variant item_value = Variant();
			if (cs == SELECT_IMPORT_FULL) {
				item_value = base_theme->get_theme_item(ti.data_type, ti.item_name, ti.type_name);
			} else {
				switch (ti.data_type) {
					case Theme::DATA_TYPE_COLOR:
						item_value = Color();
						break;
					case Theme::DATA_TYPE_CONSTANT:
						item_value = 0;
						break;
					case Theme::DATA_TYPE_FONT:
						item_value = Ref<Font>();
						break;
					case Theme::DATA_TYPE_FONT_SIZE:
						item_value = -1;
						break;
					case Theme::DATA_TYPE_ICON:
						item_value = Ref<Texture2D>();
						break;
					case Theme::DATA_TYPE_STYLEBOX:
						item_value = Ref<StyleBox>();
						break;