### 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
editable_info = TTR("This resource belongs to a scene that was instantiated or inherited.\nChanges to it must be made inside the original scene.");
					}
				}
			} else {
				if (FileAccess::exists(base_path + ".import")) {
					editable_info = TTR("This resource belongs to a scene that was imported, so it's not editable.\nPlease read the documentation relevant to importing scenes to better understand this workflow.");
				}
			}
		} else if (current_res->get_path().is_resource_file()) {
			if (FileAccess::exists(current_res->get_path() + ".import")) {
				editable_info = TTR("This resource was imported, so it's not editable. Change its settings in the import panel and then re-import.");
			}
		}
	} else if (is_node) {
		Node *current_node = Object::cast_to<Node>(current_obj);
		ERR_FAIL_COND(!current_node);
		InspectorDock::get_inspector_singleton()->edit(current_node);
		if (current_node->is_inside_tree()) {
			NodeDock::get_singleton()->set_node(current_node);
			SceneTreeDock::get_singleton()->set_selected(current_node);
			InspectorDock::get_singleton()->update(current_node);
			if (!inspector_only && !skip_main_plugin) {
				skip_main_plugin = stay_in_script_editor_on_node_selected && ScriptEditor::get_singleton()->is_visible_in_tree();
			}
		} else {
			NodeDock::get_singleton()->set_node(nullptr);
			SceneTreeDock::get_singleton()->set_selected(nullptr);
			InspectorDock::get_singleton()->update(nullptr);
		}
		if (get_edited_scene() && !get_edited_scene()->get_scene_file_path().is_empty()) {