diff --git a/starlette/responses.py b/starlette/responses.py
index a6ebe8c..4390c29 100644
--- a/starlette/responses.py
+++ b/starlette/responses.py
@@ -31,13 +31,16 @@ class Response:
 
     def __init__(
         self,
-        content: typing.Any,
+        content: typing.Any = None,
         status_code: int = 200,
         headers: dict = None,
         media_type: str = None,
         background: BackgroundTask = None,
     ) -> None:
-        self.body = self.render(content)
+        if content is None:
+            self.body = b""
+        else:
+            self.body = self.render(content)
         self.status_code = status_code
         if media_type is not None:
             self.media_type = media_type
@@ -63,8 +66,8 @@ class Response:
             populate_content_length = b"content-length" in keys
             populate_content_type = b"content-type" in keys
 
-        body = getattr(self, "body", None)
-        if body is not None and populate_content_length:
+        body = getattr(self, "body", b"")
+        if body and populate_content_length:
             content_length = str(len(body))
             raw_headers.append((b"content-length", content_length.encode("latin-1")))
 

the raw "Response" should'nt mandatory a content ... no ?
I need to manage myself the etag/304 response ...

to send a 304 if-none-match, I use : 

    Response(status_code=304,content="",headers=rheaders)

But the body content should not be written ... here the content is mandatory : None cause troubble, and empty string is an empty string ...


diff --git a/tests/test_responses.py b/tests/test_responses.py
index 7e23e29..e68958e 100644
--- a/tests/test_responses.py
+++ b/tests/test_responses.py
@@ -126,11 +126,11 @@ def test_response_headers():
 
 def test_response_phrase():
     def app(scope):
-        return Response(b"", status_code=200)
+        return Response(status_code=204)
 
     client = TestClient(app)
     response = client.get("/")
-    assert response.reason == "OK"
+    assert response.reason == "No Content"
 
     def app(scope):
         return Response(b"", status_code=123)

pip install -e .[full]
parse_log_pytest
requirements.txt
3.7
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
aiofiles==23.2.1
Babel==2.14.0
black==23.3.0
certifi @ file:///croot/certifi_1671487769961/work/certifi
charset-normalizer==3.4.1
click==8.1.8
codecov==2.1.13
colorama==0.4.6
coverage==7.2.7
exceptiongroup==1.2.2
ghp-import==2.1.0
graphene==3.4.3
graphql-core==3.2.6
graphql-relay==3.2.0
idna==3.10
importlib-metadata==6.7.0
iniconfig==2.0.0
isort==5.11.5
itsdangerous==2.1.2
Jinja2==3.1.6
Markdown==3.4.4
MarkupSafe==2.1.5
mergedeep==1.3.4
mkdocs==1.5.3
mkdocs-material==9.2.7
mkdocs-material-extensions==1.2
mypy==1.4.1
mypy-extensions==1.0.0
packaging==24.0
paginate==0.5.7
pathspec==0.11.2
platformdirs==4.0.0
pluggy==1.2.0
Pygments==2.17.2
pymdown-extensions==10.2.1
pytest==7.4.4
pytest-cov==4.1.0
python-dateutil==2.9.0.post0
python-multipart==0.0.8
pytz==2025.2
PyYAML==6.0.1
pyyaml_env_tag==0.1
regex==2022.10.31
requests==2.31.0
six==1.17.0
-e git+https://github.com/encode/starlette.git@3a16d660490b54daad5711749fa00fd7a0970b4e#egg=starlette
tomli==2.0.1
typed-ast==1.5.5
typing_extensions==4.7.1
ujson==5.7.0
urllib3==2.0.7
watchdog==3.0.0
zipp==3.15.0

name: starlette
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2022.12.7=py37h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=22.3.1=py37h06a4308_0
  - python=3.7.16=h7a1cb2a_0
  - readline=8.2=h5eee18b_0
  - setuptools=65.6.3=py37h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.38.4=py37h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - aiofiles==23.2.1
      - babel==2.14.0
      - black==23.3.0
      - charset-normalizer==3.4.1
      - click==8.1.8
      - codecov==2.1.13
      - colorama==0.4.6
      - coverage==7.2.7
      - exceptiongroup==1.2.2
      - ghp-import==2.1.0
      - graphene==3.4.3
      - graphql-core==3.2.6
      - graphql-relay==3.2.0
      - idna==3.10
      - importlib-metadata==6.7.0
      - iniconfig==2.0.0
      - isort==5.11.5
      - itsdangerous==2.1.2
      - jinja2==3.1.6
      - markdown==3.4.4
      - markupsafe==2.1.5
      - mergedeep==1.3.4
      - mkdocs==1.5.3
      - mkdocs-material==9.2.7
      - mkdocs-material-extensions==1.2
      - mypy==1.4.1
      - mypy-extensions==1.0.0
      - packaging==24.0
      - paginate==0.5.7
      - pathspec==0.11.2
      - platformdirs==4.0.0
      - pluggy==1.2.0
      - pygments==2.17.2
      - pymdown-extensions==10.2.1
      - pytest==7.4.4
      - pytest-cov==4.1.0
      - python-dateutil==2.9.0.post0
      - python-multipart==0.0.8
      - pytz==2025.2
      - pyyaml==6.0.1
      - pyyaml-env-tag==0.1
      - regex==2022.10.31
      - requests==2.31.0
      - six==1.17.0
      - tomli==2.0.1
      - typed-ast==1.5.5
      - typing-extensions==4.7.1
      - ujson==5.7.0
      - urllib3==2.0.7
      - watchdog==3.0.0
      - zipp==3.15.0
prefix: /opt/conda/envs/starlette

tests/test_responses.py::test_response_phrase
tests/test_responses.py::test_text_response tests/test_responses.py::test_bytes_response tests/test_responses.py::test_ujson_response tests/test_responses.py::test_redirect_response tests/test_responses.py::test_streaming_response tests/test_responses.py::test_response_headers tests/test_responses.py::test_file_response tests/test_responses.py::test_file_response_with_directory_raises_error tests/test_responses.py::test_file_response_with_missing_file_raises_error tests/test_responses.py::test_set_cookie tests/test_responses.py::test_delete_cookie
starlette/responses.py
starlette/responses.py