### 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
file->set_current_path(scene->get_scene_file_path());
			};
			file->set_title(TTR("Pick a Main Scene"));
			file->popup_file_dialog();
		} break;
		case HELP_SEARCH: {
			emit_signal(SNAME("request_help_search"), "");
		} break;
		case HELP_COMMAND_PALETTE: {
			command_palette->open_popup();
		} break;
		case HELP_DOCS: {
			OS::get_singleton()->shell_open(VERSION_DOCS_URL "/");
		} break;
		case HELP_QA: {
			OS::get_singleton()->shell_open("https:godotengine.org/qa/");
		} break;
		case HELP_REPORT_A_BUG: {
			OS::get_singleton()->shell_open("https:github.com/godotengine/godot/issues");
		} break;
		case HELP_COPY_SYSTEM_INFO: {
			String info = _get_system_info();
			DisplayServer::get_singleton()->clipboard_set(info);
		} break;
		case HELP_SUGGEST_A_FEATURE: {
			OS::get_singleton()->shell_open("https:github.com/godotengine/godot-proposals#readme");
		} break;
		case HELP_SEND_DOCS_FEEDBACK: {
			OS::get_singleton()->shell_open("https:github.com/godotengine/godot-docs/issues");
		} break;