diff --git a/my/core/query.py b/my/core/query.py
index f78a1f7..4e00569 100644
--- a/my/core/query.py
+++ b/my/core/query.py
@@ -52,9 +52,9 @@ def locate_function(module_name: str, function_name: str) -> Callable[[], Iterab
     """
     try:
         mod = importlib.import_module(module_name)
-        for (fname, func) in inspect.getmembers(mod, inspect.isfunction):
+        for (fname, f) in inspect.getmembers(mod, inspect.isfunction):
             if fname == function_name:
-                return func
+                return f
         # in case the function is defined dynamically,
         # like with a globals().setdefault(...) or a module-level __getattr__ function
         func = getattr(mod, function_name, None)
diff --git a/my/core/serialize.py b/my/core/serialize.py
index 1ef7bc0..c5f4cba 100644
--- a/my/core/serialize.py
+++ b/my/core/serialize.py
@@ -62,10 +62,9 @@ def _dumps_factory(**kwargs) -> Callable[[Any], str]:
     if _additional_default is not None and callable(_additional_default):
 
         def wrapped_default(obj: Any) -> Any:
+            assert _additional_default is not None
             try:
-                # hmm... shouldn't mypy know that _additional_default is not None here?
-                # assert _additional_default is not None
-                return _additional_default(obj)  # type: ignore[misc]
+                return _additional_default(obj)
             except TypeError:
                 # expected TypeError, signifies couldn't be encoded by custom
                 # serializer function. Try _default_encode from here