From 167fed622c47793bf7cfb1d88902a11037bc345d Mon Sep 17 00:00:00 2001
From: Viicos <65306057+Viicos@users.noreply.github.com>
Date: Wed, 12 Apr 2023 13:53:18 +0200
Subject: [PATCH 1/3] Fix handling of value when multiple files in form-data

It appears that the value list extracted from the `FormData`
is not necessarily composed of `UploadFile` instances.
---
 fastapi/dependencies/utils.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py
index c581348c9..e5c7d777c 100644
--- a/fastapi/dependencies/utils.py
+++ b/fastapi/dependencies/utils.py
@@ -778,7 +778,10 @@ async def request_body_to_args(
 
                 async with anyio.create_task_group() as tg:
                     for sub_value in value:
-                        tg.start_soon(process_fn, sub_value.read)
+                        if isinstance(sub_value, UploadFile):
+                            tg.start_soon(process_fn, sub_value.read)
+                        else:
+                            results.append(sub_value)
                 value = sequence_shape_to_type[field.shape](results)
 
             v_, errors_ = field.validate(value, values, loc=loc)

From 39cb6471f758fdeef8d19af520722d5706529fd0 Mon Sep 17 00:00:00 2001
From: Yurii Motov <yurii.motov.monte@gmail.com>
Date: Thu, 12 Feb 2026 16:32:11 +0100
Subject: [PATCH 2/3] Add test

---
 tests/test_optional_file_list.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tests/test_optional_file_list.py b/tests/test_optional_file_list.py
index 686025864..f237346ee 100644
--- a/tests/test_optional_file_list.py
+++ b/tests/test_optional_file_list.py
@@ -1,5 +1,3 @@
-from typing import Optional
-
 from fastapi import FastAPI, File
 from fastapi.testclient import TestClient
 
@@ -7,7 +5,7 @@ app = FastAPI()
 
 
 @app.post("/files")
-async def upload_files(files: Optional[list[bytes]] = File(None)):
+async def upload_files(files: list[bytes] | None = File(None)):
     if files is None:
         return {"files_count": 0}
     return {"files_count": len(files), "sizes": [len(f) for f in files]}
@@ -28,3 +26,13 @@ def test_optional_bytes_list_no_files():
     response = client.post("/files")
     assert response.status_code == 200
     assert response.json() == {"files_count": 0}
+
+
+def test_optional_bytes_list_send_empty_str():
+    client = TestClient(app)
+    response = client.post(
+        "/files",
+        files=[("files", b"")],
+    )
+    assert response.status_code == 200
+    assert response.json() == {"files_count": 1, "sizes": [0]}

From c524dd41e0caa45175394290ab8e6d0ff67dab2f Mon Sep 17 00:00:00 2001
From: Yurii Motov <yurii.motov.monte@gmail.com>
Date: Thu, 12 Feb 2026 16:46:01 +0100
Subject: [PATCH 3/3] Fix test to send empty string instead of empty file

---
 tests/test_optional_file_list.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_optional_file_list.py b/tests/test_optional_file_list.py
index f237346ee..0e11a262a 100644
--- a/tests/test_optional_file_list.py
+++ b/tests/test_optional_file_list.py
@@ -32,7 +32,7 @@ def test_optional_bytes_list_send_empty_str():
     client = TestClient(app)
     response = client.post(
         "/files",
-        files=[("files", b"")],
+        data={"files": ""},
     )
     assert response.status_code == 200
     assert response.json() == {"files_count": 1, "sizes": [0]}