feat(content): allow multipart requests without files.

httpx/_content.py

@@ -208,7 +208,7 @@ def encode_request(
 
     if content is not None:
         return encode_content(content)
-    elif files:
+    elif files is not None:
         return encode_multipart_data(data or {}, files, boundary)
     elif data:
         return encode_urlencoded_data(data)

httpx/_main.py

@@ -483,7 +483,7 @@ def main(
                 params=list(params),
                 content=content,
                 data=dict(data),
-                files=files,  # type: ignore
+                files=files or None,  # type: ignore
                 json=json,
                 headers=headers,
                 cookies=dict(cookies),

tests/test_content.py

@@ -5,6 +5,7 @@
 
 import httpx
 
+
 method = "POST"
 url = "https://www.example.com"
 
@@ -344,7 +345,7 @@ async def test_multipart_data_and_files_content():
 
 @pytest.mark.anyio
 async def test_empty_request():
-    request = httpx.Request(method, url, data={}, files={})
+    request = httpx.Request(method, url, data={})
     assert isinstance(request.stream, typing.Iterable)
     assert isinstance(request.stream, typing.AsyncIterable)
 
@@ -516,3 +517,13 @@ def test_allow_nan_false():
         ValueError, match="Out of range float values are not JSON compliant"
     ):
         httpx.Response(200, json=data_with_inf)
+
+
+def test_encode_request_with_data_and_empty_files():
+    request = httpx.Request(
+        url="https://www.example.com", method="POST", data={"key": "value"}, files={}
+    )
+    assert request.headers["Content-Type"].startswith("multipart/form-data; boundary=")
+    request.read()
+    assert b'Content-Disposition: form-data; name="key"' in request.content
+    assert b"value" in request.content