Improve type annotations of Map.update and MapMutation.update

Author: hukkinj1

immutables/_map.pyi

@@ -7,6 +7,7 @@ from typing import Literal
 from typing import Mapping
 from typing import MutableMapping
 from typing import NoReturn
+from typing import overload
 from typing import Tuple
 from typing import Type
 from typing import TypeVar
@@ -46,8 +47,11 @@ class Map(Mapping[K, V]):
     def __reduce__(self) -> Tuple[Type[Map], Tuple[dict]]: ...
     def __len__(self) -> int: ...
     def __eq__(self, other: Any) -> bool: ...
+    @overload
+    def update(self, **kw: V) -> Map[str, V]: ...
+    @overload
     def update(
-        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]] = ..., **kw: V
+        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]], **kw: V
     ) -> Map[K, V]: ...
     def mutate(self) -> MapMutation[K, V]: ...
     def set(self, key: K, val: V) -> Map[K, V]: ...
@@ -79,9 +83,12 @@ class MapMutation(MutableMapping[K, V]):
     def get(self, key: K, default: D = ...) -> Union[V, D]: ...
     def __getitem__(self, key: K) -> V: ...
     def __contains__(self, key: Any) -> bool: ...
+    @overload
+    def update(self, **kw: V) -> None: ...
+    @overload
     def update(
-        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]] = ..., **kw: V
-    ): ...
+        self, col: Union[Mapping[K, V], Iterable[Tuple[K, V]]], **kw: V
+    ) -> None: ...
     def finish(self) -> Map[K, V]: ...
     def __len__(self) -> int: ...
     def __eq__(self, other: Any) -> bool: ...