### 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
String source_scene = get_edited_scene()->get_scene_file_path();
			if (FileAccess::exists(source_scene + ".import")) {
				editable_info = TTR("This scene was imported, so changes to it won't be kept.\nInstantiating or inheriting it will allow you to make changes to it.\nPlease read the documentation relevant to importing scenes to better understand this workflow.");
				info_is_warning = true;
			}
		}
	} else {
		Node *selected_node = nullptr;
		if (current_obj->is_class("EditorDebuggerRemoteObject")) {
			disable_folding = true;
		} else if (current_obj->is_class("MultiNodeEdit")) {
			Node *scene = get_edited_scene();
			if (scene) {
				MultiNodeEdit *multi_node_edit = Object::cast_to<MultiNodeEdit>(current_obj);
				int node_count = multi_node_edit->get_node_count();
				if (node_count > 0) {
					List<Node *> multi_nodes;
					for (int node_index = 0; node_index < node_count; ++node_index) {
						Node *node = scene->get_node(multi_node_edit->get_node(node_index));
						if (node) {
							multi_nodes.push_back(node);
						}
					}
					if (!multi_nodes.is_empty()) {
						
						multi_nodes.sort_custom<Node::Comparator>();
						selected_node = multi_nodes.front()->get();
					}
				}
			}