### 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
singleton->progress_hb->add_task(p_task, p_label, p_steps);
}
void EditorNode::progress_task_step_bg(const String &p_task, int p_step) {
	singleton->progress_hb->task_step(p_task, p_step);
}
void EditorNode::progress_end_task_bg(const String &p_task) {
	singleton->progress_hb->end_task(p_task);
}
String EditorNode::_get_system_info() const {
	String distribution_name = OS::get_singleton()->get_distribution_name();
	if (distribution_name.is_empty()) {
		distribution_name = OS::get_singleton()->get_name();
	}
	if (distribution_name.is_empty()) {
		distribution_name = "Other";
	}
	const String distribution_version = OS::get_singleton()->get_version();
	String godot_version = "Godot v" + String(VERSION_FULL_CONFIG);
	if (String(VERSION_BUILD) != "official") {
		String hash = String(VERSION_HASH);
		hash = hash.is_empty() ? String("unknown") : vformat("(%s)", hash.left(9));
		godot_version += " " + hash;
	}
	String driver_name = GLOBAL_GET("rendering/rendering_device/driver");
	String rendering_method = GLOBAL_GET("rendering/renderer/rendering_method");
	const String rendering_device_name = RenderingServer::get_singleton()->get_video_adapter_name();
	RenderingDevice::DeviceType device_type = RenderingServer::get_singleton()->get_video_adapter_type();
	String device_type_string;
	switch (device_type) {