eschutho opened a new pull request, #35808:
URL: https://github.com/apache/superset/pull/35808
### SUMMARY
Fixes an `AttributeError: 'NoneType' object has no attribute 'read'` that
occurred when the dashboard thumbnail endpoint attempted to serve an invalid or
corrupted BytesIO object.
**Root Cause:**
When retrieving cached thumbnail images, the endpoint would pass a BytesIO
object to `FileWrapper`, but in some edge cases (corrupt cache, empty data,
etc.), this object would be `None` or invalid. The error only manifested at the
WSGI layer when attempting to read from the file, causing server errors instead
of graceful 404 responses.
**Changes:**
- Added validation to ensure BytesIO contains actual data (nbytes > 0)
- Reset file position with `seek(0)` before passing to FileWrapper
- Added comprehensive exception handling with detailed error logging
- All invalid thumbnail states now return proper 404 responses
### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
N/A - Backend fix with no UI changes
### TESTING INSTRUCTIONS
1. Trigger the thumbnail endpoint with a corrupted or missing cache entry:
```
GET /api/v1/dashboard/44/thumbnail/{digest}/
```
2. Verify the endpoint returns a 404 response instead of a 500 error
3. Check logs for warning messages when thumbnails are invalid/empty
4. Verify valid thumbnails still work correctly
### ADDITIONAL INFORMATION
- [ ] Has associated issue:
- [ ] Required feature flags: `THUMBNAILS` (existing)
- [ ] Changes UI
- [ ] Includes DB Migration
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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