Ensure Response is True even when map is empty (#10172)

Fixes #10119

Technically a breaking change, but I can't imagine anyone depending on
this.

CHANGES/10119.bugfix.rst

@@ -0,0 +1 @@
+Response is now always True, instead of using MutableMapping behaviour (False when map is empty)

aiohttp/web_response.py

@@ -504,6 +504,9 @@ def __hash__(self) -> int:
     def __eq__(self, other: object) -> bool:
         return self is other
 
+    def __bool__(self) -> bool:
+        return True
+
 
 class Response(StreamResponse):
 

tests/test_web_request.py

@@ -287,6 +287,7 @@ def test_match_info() -> None:
 def test_request_is_mutable_mapping() -> None:
     req = make_mocked_request("GET", "/")
     assert isinstance(req, MutableMapping)
+    assert req  # even when the MutableMapping is empty, request should always be True
     req["key"] = "value"
     assert "value" == req["key"]
 

tests/test_web_response.py

@@ -93,6 +93,7 @@ def test_stream_response_eq() -> None:
 def test_stream_response_is_mutable_mapping() -> None:
     resp = web.StreamResponse()
     assert isinstance(resp, collections.abc.MutableMapping)
+    assert resp  # even when the MutableMapping is empty, response should always be True
     resp["key"] = "value"
     assert "value" == resp["key"]