If no thumbnail of the requested type exists, return a 404 instead of erroring. This doesn't quite match the spec (which does not define what happens if no thumbnail can be found), but is consistent with what Synapse already does.  | 
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|---|---|---|
| .. | ||
| __init__.py | ||
| test_base.py | ||
| test_media_storage.py | ||
| test_url_preview.py | ||