fix: Optional[UploadFile] should be None when no file submitted in multipart form#4659
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provinzkraut merged 4 commits intolitestar-org:mainfrom Apr 2, 2026
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…n no file submitted
When a browser submits a multipart form without selecting a file, the field
is sent as an empty string (""). Since 2.18.0 (PR litestar-org#4271 which fixed litestar-org#4204),
this empty string is no longer converted to None, causing validation to fail
for Optional[UploadFile] fields with a 400 error.
Fix: in _extract_multipart, before the type-hints loop, detect when a field
value is "" and the expected type is Optional[UploadFile] (or a subclass),
and replace the empty string with None before it reaches the conversion layer.
Fixes litestar-org#4647
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #4659 +/- ##
=======================================
Coverage 67.32% 67.33%
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Files 292 292
Lines 14933 14938 +5
Branches 1673 1675 +2
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+ Hits 10054 10058 +4
Misses 4743 4743
- Partials 136 137 +1 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Contributor
Wouldn't this result in a weird exception if the field is annotated as (required) UploadFile and no file is uploaded nonetheless? I think getting a None in those cases is better than an empty string for consistency reasons |
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Description
When a browser submits a multipart form without selecting a file, the file field
arrives as an empty string (
""). Since 2.18.0 (PR fix: Preserve empty strings in multipart/form-data requests (#4204) #4271 which fixed Bug: Empty strings in multipart/form-data requests are converted to None #4204),this empty string is preserved instead of being converted to
None, causing a400validation error forOptional[UploadFile]fields.Fix: in
_extract_multipart(litestar/_kwargs/extractors.py), inside thetype-hints loop, detect when a field value is
""and the annotated type isOptional[UploadFile](or a subclass). Replace the empty string withNonebefore it reaches the conversion layer — an empty file input means "no file
selected", which matches the semantics of an
Optionalupload field.Regression test added in
tests/unit/test_kwargs/test_multipart_data.py.Closes
Closes #4647
📚 Documentation preview 📚: https://litestar-org.github.io/litestar-docs-preview/4659