### 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
#include "editor/import/dynamic_font_import_settings.h"
#include "editor/import/editor_import_collada.h"
#include "editor/import/resource_importer_bitmask.h"
#include "editor/import/resource_importer_bmfont.h"
#include "editor/import/resource_importer_csv_translation.h"
#include "editor/import/resource_importer_dynamic_font.h"
#include "editor/import/resource_importer_image.h"
#include "editor/import/resource_importer_imagefont.h"
#include "editor/import/resource_importer_layered_texture.h"
#include "editor/import/resource_importer_obj.h"
#include "editor/import/resource_importer_shader_file.h"
#include "editor/import/resource_importer_texture.h"
#include "editor/import/resource_importer_texture_atlas.h"
#include "editor/import/resource_importer_wav.h"
#include "editor/import/scene_import_settings.h"
#include "editor/import_dock.h"
#include "editor/inspector_dock.h"
#include "editor/multi_node_edit.h"
#include "editor/node_dock.h"
#include "editor/plugin_config_dialog.h"
#include "editor/plugins/animation_player_editor_plugin.h"
#include "editor/plugins/asset_library_editor_plugin.h"
#include "editor/plugins/canvas_item_editor_plugin.h"
#include "editor/plugins/debugger_editor_plugin.h"
#include "editor/plugins/dedicated_server_export_plugin.h"
#include "editor/plugins/editor_preview_plugins.h"
#include "editor/plugins/editor_resource_conversion_plugin.h"
#include "editor/plugins/gdextension_export_plugin.h"
#include "editor/plugins/material_editor_plugin.h"
#include "editor/plugins/mesh_library_editor_plugin.h"