fix typing

Author: q0w

src/pip/_internal/utils/misc.py

@@ -734,7 +734,7 @@ def prepare_metadata_for_build_editable(
 def merge_config_settings(
     reqs_settings: Optional[Dict[str, Union[str, List[str]]]],
     cli_settings: Optional[Dict[str, Union[str, List[str]]]],
-) -> Dict[str, Union[str, List[str]]]:
+) -> Optional[Dict[str, Union[str, List[str]]]]:
     if not reqs_settings or not cli_settings:
         return reqs_settings or cli_settings
 

tests/unit/test_utils_misc.py

@@ -15,11 +15,12 @@
         ({"foo": "bar"}, {"foo": ["baz"]}, {"foo": ["bar", "baz"]}),
         ({"foo": "bar"}, None, {"foo": "bar"}),
         (None, {"foo": ["bar"]}, {"foo": ["bar"]}),
+        (None, None, None),
     ],
 )
 def test_merge_config_settings(
     reqs: Optional[Dict[str, Union[str, List[str]]]],
     cli: Optional[Dict[str, Union[str, List[str]]]],
-    expected: Dict[str, Union[str, List[str]]],
+    expected: Optional[Dict[str, Union[str, List[str]]]],
 ) -> None:
     assert merge_config_settings(reqs, cli) == expected