### 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
Node *scene = editor_data.get_edited_scene_root();
	if (!scene) {
		return;
	}
	List<String> esl;
	p_config_file->get_section_keys("editor_states", &esl);
	Dictionary md;
	for (const String &E : esl) {
		Variant st = p_config_file->get_value("editor_states", E);
		if (st.get_type() != Variant::NIL) {
			md[E] = st;
		}
	}
	editor_data.set_editor_plugin_states(md);
}
void EditorNode::_save_editor_states(const String &p_file, int p_idx) {