### 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
case Theme::DATA_TYPE_MAX:
						break; 
				}
			}
			new_snapshot->set_theme_item(ti.data_type, ti.item_name, ti.type_name, item_value);
		}
		idx++;
	}
	
	ProgressDialog::get_singleton()->task_step("import_theme_items", TTR("Updating the editor"), idx++);
	
	ProgressDialog::get_singleton()->task_step("import_theme_items", TTR("Finalizing"), idx++);
	ProgressDialog::get_singleton()->end_task("import_theme_items");
	EditorUndoRedoManager *ur = EditorUndoRedoManager::get_singleton();
	ur->create_action(TTR("Import Theme Items"));
	ur->add_do_method(*edited_theme, "clear");
	ur->add_do_method(*edited_theme, "merge_with", new_snapshot);
	ur->add_undo_method(*edited_theme, "clear");
	ur->add_undo_method(*edited_theme, "merge_with", old_snapshot);
	ur->add_do_method(this, "emit_signal", SNAME("items_imported"));
	ur->add_undo_method(this, "emit_signal", SNAME("items_imported"));
	ur->commit_action();
}
void ThemeItemImportTree::set_edited_theme(const Ref<Theme> &p_theme) {
	edited_theme = p_theme;
}
void ThemeItemImportTree::set_base_theme(const Ref<Theme> &p_theme) {
	base_theme = p_theme;
}
void ThemeItemImportTree::reset_item_tree() {