Fix query_param_matcher not matching empty query parameter values (#787)

_parse_request_params calls parse_qsl without keep_blank_values=True,
so query parameters with empty string values (e.g. ?bar=) are silently
dropped. This causes query_param_matcher({"bar": ""}) to never match.

Fixes #778

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: worksbyfriday

responses/__init__.py

@@ -1051,7 +1051,10 @@ def _parse_request_params(
         self, url: str
     ) -> Dict[str, Union[str, int, float, List[Optional[Union[str, int, float]]]]]:
         params: Dict[str, Union[str, int, float, List[Any]]] = {}
-        for key, val in groupby(parse_qsl(urlsplit(url).query), lambda kv: kv[0]):
+        for key, val in groupby(
+            parse_qsl(urlsplit(url).query, keep_blank_values=True),
+            lambda kv: kv[0],
+        ):
             values = list(map(lambda x: x[1], val))
             if len(values) == 1:
                 values = values[0]  # type: ignore[assignment]

responses/tests/test_matchers.py

@@ -260,6 +260,24 @@ def run():
     assert_reset()
 
 
+def test_query_param_matcher_empty_value():
+    @responses.activate
+    def run():
+        responses.add(
+            responses.GET,
+            "https://example.com/foo",
+            match=[
+                matchers.query_param_matcher({"bar": ""}),
+            ],
+            json={},
+        )
+        resp = requests.get("https://example.com/foo?bar=")
+        assert resp.status_code == 200
+
+    run()
+    assert_reset()
+
+
 def test_query_param_matcher_loose():
     @responses.activate
     def run():