### 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
project_run_bar->stop_child_process(p_pid);
}
Ref<Script> EditorNode::get_object_custom_type_base(const Object *p_object) const {
	ERR_FAIL_COND_V(!p_object, nullptr);
	Ref<Script> scr = p_object->get_script();
	if (scr.is_valid()) {
		
		
		
		
		
		
		StringName base = scr->get_instance_base_type();
		if (base != StringName() && EditorNode::get_editor_data().get_custom_types().has(base)) {
			const Vector<EditorData::CustomType> &types = EditorNode::get_editor_data().get_custom_types()[base];
			Ref<Script> base_scr = scr;
			while (base_scr.is_valid()) {
				for (int i = 0; i < types.size(); ++i) {
					if (types[i].script == base_scr) {
						return types[i].script;
					}
				}
				base_scr = base_scr->get_base_script();
			}
		}
	}
	return nullptr;
}
StringName EditorNode::get_object_custom_type_name(const Object *p_object) const {