feeling_lucky() (dice button) crashes the player by writing data_source.Default = null

[SoplosLinux]

Environment

• Hidamari v3.7 (Flatpak, Flathub)
• Non-GNOME X11 session (XFCE-based)
• System info reported by Hidamari on startup: is_gnome = False, is_wayland = False, is_flatpak = True

Steps to reproduce

1. Start Hidamari with a video already configured (config.json has both data_source.Default and data_source.<monitor> pointing to a valid file).
2. Click the dice icon ("I'm feeling lucky") in the main window, or call the D-Bus method directly:

gdbus call --session --dest io.github.jeffshee.Hidamari.server --object-path /io/github/jeffshee/Hidamari/server --method io.github.jeffshee.hidamari.server.feeling_lucky

3. The player process crashes and the video wallpaper stops.

What happens

When a new random video is picked, the config is saved with the new path under the monitor-specific key (e.g. eDP-1), but Default gets reset to null:

Before:

"data_source": {
   "Default": "/home/soplos/Vídeos/Hidamari/c9fa0212b8_sunset-serenity-pavilion-asian-lake-live-wallpaper-wallsflow-com.mp4",
   "eDP-1": "/home/soplos/Vídeos/Hidamari/c9fa0212b8_sunset-serenity-pavilion-asian-lake-live-wallpaper-wallsflow-com.mp4"
}

After clicking the dice:

"data_source": {
   "Default": null,
   "eDP-1": "/home/soplos/Vídeos/Hidamari/815bc7130a_forgotten-train-station.mp4"
}

The hidamari-player-1 subprocess then calls reload_config(), which calls _checkDefaultSource() (utils.py:410), which does os.path.isfile(default_source) where default_source is None, raising:

TypeError: stat: path should be string, bytes, os.PathLike or integer, not NoneType

Full traceback

Process hidamari-player-1:
Traceback (most recent call last):
  File "/usr/lib/python3.13/multiprocessing/process.py", line 313, in _bootstrap
    self.run()
  File "/usr/lib/python3.13/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/app/share/hidamari/hidamari/player/video_player.py", line 748, in main
    app = VideoPlayer()
  File "/app/share/hidamari/hidamari/player/video_player.py", line 335, in __init__
    self.reload_config()
  File "/app/share/hidamari/hidamari/player/video_player.py", line 724, in reload_config
    self.config = ConfigUtil().load()
  File "/app/share/hidamari/hidamari/utils.py", line 437, in load
    self._checkDefaultSource(config)
  File "/app/share/hidamari/hidamari/utils.py", line 410, in _checkDefaultSource
    if mode == MODE_VIDEO and not os.path.isfile(default_source):
  File "<frozen genericpath>", line 39, in isfile
TypeError: stat: path should be string, bytes, os.PathLike or integer, not NoneType

Additional notes

• After this crash, the app's own --reset flag does not help, since _load_config() (which reads the broken config) runs before the reset logic can apply.
• The corrupted config also breaks every subsequent launch, including via autostart, since _checkDefaultSource() is called on every startup while mode is MODE_VIDEO.
• Manually fixing data_source.Default to match the current per-monitor value in config.json restores normal startup, until the dice button is used again.