### 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
case Variant::ARRAY: {
				Array varray = obj->get(E.name);
				int len = varray.size();
				for (int i = 0; i < len; i++) {
					const Variant &v = varray.get(i);
					Ref<Resource> res = v;
					if (_find_and_save_resource(res, processed, flags)) {
						ret_changed = true;
					}
				}
			} break;
			case Variant::DICTIONARY: {
				Dictionary d = obj->get(E.name);
				List<Variant> keys;
				d.get_key_list(&keys);
				for (const Variant &F : keys) {
					Variant v = d[F];
					Ref<Resource> res = v;
					if (_find_and_save_resource(res, processed, flags)) {
						ret_changed = true;
					}
				}
			} break;
			default: {
			}
		}
	}
	return ret_changed;
}
void EditorNode::_save_edited_subresources(Node *scene, HashMap<Ref<Resource>, bool> &processed, int32_t flags) {