Message.get_content_charset() returns None by default (#9344)

Author: srittau

stdlib/email/message.pyi

@@ -5,7 +5,7 @@ from email.charset import Charset
 from email.contentmanager import ContentManager
 from email.errors import MessageDefect
 from email.policy import Policy
-from typing import Any, TypeVar
+from typing import Any, TypeVar, overload
 from typing_extensions import TypeAlias
 
 __all__ = ["Message", "EmailMessage"]
@@ -54,7 +54,10 @@ class Message:
     def get_filename(self, failobj: _T = ...) -> _T | str: ...
     def get_boundary(self, failobj: _T = ...) -> _T | str: ...
     def set_boundary(self, boundary: str) -> None: ...
-    def get_content_charset(self, failobj: _T = ...) -> _T | str: ...
+    @overload
+    def get_content_charset(self) -> str | None: ...
+    @overload
+    def get_content_charset(self, failobj: _T) -> str | _T: ...
     def get_charsets(self, failobj: _T = ...) -> _T | list[str]: ...
     def walk(self: Self) -> Generator[Self, None, None]: ...
     def get_content_disposition(self) -> str | None: ...