Error about asset not existing when it does

[cheshire137]

I'm getting an odd error when I try to run the app about how an asset file doesn't exist. The asset in question changes when I run the app (sometimes it's summer, sometimes winter, etc.), and it definitely exists. 🤔 Here's my backtrace:

% SDV_APP_SETTINGS=development FLASK_APP=runserver.py flask run
 * Serving Flask app "runserver.py"
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
2019-02-17 13:22:19,803 [INFO] UploadFarm.init - Creating flask app...
2019-02-17 13:22:19,804 [INFO] UploadFarm.init - Config name not supplied, searching environment
2019-02-17 13:22:19,804 [INFO] UploadFarm.init - Config name set to: development
2019-02-17 13:22:19,804 [INFO] UploadFarm.init - Initialising extensions
2019-02-17 13:22:19,817 [INFO] UploadFarm.init - Application set to use Postgres
Traceback (most recent call last):
  File "/usr/local/bin/flask", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 894, in main
    cli.main(args=args, prog_name=name)
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 557, in main
    return super(FlaskGroup, self).main(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/click/decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 767, in run_command
    app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 293, in __init__
    self._load_unlocked()
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 317, in _load_unlocked
    self._app = rv = self.loader()
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 372, in load_app
    app = locate_app(self, import_name, name)
  File "/usr/local/lib/python3.7/site-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/runserver.py", line 13, in <module>
    from sdv import app
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/sdv/__init__.py", line 156, in <module>
    import sdv.imageDrone  # noqa
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/sdv/imageDrone.py", line 14, in <module>
    from sdv.imagegeneration.avatar import generateAvatar
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/sdv/imagegeneration/avatar.py", line 5, in <module>
    from .assets import loadAvatarAssets
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/sdv/imagegeneration/assets.py", line 21, in <module>
    for season in SEASONS
  File "/Users/cheshire137/code/Sketchy502/SDV-Summary/sdv/imagegeneration/assets.py", line 21, in <dictcomp>
    for season in SEASONS
  File "/usr/local/lib/python3.7/site-packages/PIL/Image.py", line 2477, in open
    fp = builtins.open(filename, "rb")
FileNotFoundError: [Errno 2] No such file or directory: 'sdv/assets/farm/summer_outdoorsTileSheet.png'

And here's the contents of that directory, showing that sdv/assets/farm/summer_outdoorsTileSheet.png does exist:

code/Sketchy502/SDV-Summary at wonderland (master ✗)
% ls sdv/assets/farm/
buildings                    spring_outdoorsTileSheet.png winter_outdoorsTileSheet.png
fall_outdoorsTileSheet.png   summer_outdoorsTileSheet.png
grass                        trees

The only thing I can think of is that I haven't put all the asset files in the sdv/assets/ directory yet, and maybe this error message is misleading in that it says the summer tile sheet isn't there, when really it's a different asset that isn't there that it expects. Any thoughts?