No Canvas Files option when launching an unconfigured assignment in Canvas

1. Create an assignment in Canvas
2. Edit the assignment and manually remove the the `?url` or the `?canvas_file` and `&file_id` query params from the URL (so the "external tool URL" becomes just `http://localhost:8001/lti_launches`)
3. Launch the assignment (you must be logged in as a teacher)

You'll see the file picker UI for choosing the assignment's document but only the URL and Google Drive options will be present -- Canvas files is missing.