### Godot version

4.1 rc3

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

This™
![image](https://github.com/godotengine/godot/assets/2223172/cb33110f-a5b0-400a-951f-3fa425f05714)

It can still happen, but it's more difficult to trigger.

### Steps to reproduce

1. Create a new scene with a Control node
2. Add Theme to the Control
3. Open Theme Editor
4. Clear the `theme` property in Control
5. Save, with Theme Editor opened
6. Restart

### Minimal reproduction project

N/A
execute_outputs->set_context_menu_enabled(true);
	execute_output_dialog = memnew(AcceptDialog);
	execute_output_dialog->set_unparent_when_invisible(true);
	execute_output_dialog->add_child(execute_outputs);
	execute_output_dialog->set_title("");
	EditorFileSystem::get_singleton()->connect("sources_changed", callable_mp(this, &EditorNode::_sources_changed));
	EditorFileSystem::get_singleton()->connect("filesystem_changed", callable_mp(this, &EditorNode::_fs_changed));
	EditorFileSystem::get_singleton()->connect("resources_reimported", callable_mp(this, &EditorNode::_resources_reimported));
	EditorFileSystem::get_singleton()->connect("resources_reload", callable_mp(this, &EditorNode::_resources_changed));
	_build_icon_type_cache();
	pick_main_scene = memnew(ConfirmationDialog);
	gui_base->add_child(pick_main_scene);
	pick_main_scene->set_ok_button_text(TTR("Select"));
	pick_main_scene->connect("confirmed", callable_mp(this, &EditorNode::_menu_option).bind(SETTINGS_PICK_MAIN_SCENE));
	select_current_scene_button = pick_main_scene->add_button(TTR("Select Current"), true, "select_current");
	pick_main_scene->connect("custom_action", callable_mp(this, &EditorNode::_pick_main_scene_custom_action));
	for (int i = 0; i < _init_callbacks.size(); i++) {
		_init_callbacks[i]();
	}
	editor_data.add_edited_scene(-1);
	editor_data.set_edited_scene(0);
	_update_scene_tabs();
	ImportDock::get_singleton()->initialize_import_options();
	FileAccess::set_file_close_fail_notify_callback(_file_access_close_error_notify);
	print_handler.printfunc = _print_handler;
	print_handler.userdata = this;
	add_print_handler(&print_handler);
	ResourceSaver::set_save_callback(_resource_saved);
	ResourceLoader::set_load_callback(_resource_loaded);