email.message: Fix invalid TypeVar usage; add some default values (#9620)

Author: AlexWaygood

stdlib/email/message.pyi

@@ -38,27 +38,52 @@ class Message:
     def keys(self) -> list[str]: ...
     def values(self) -> list[_HeaderType]: ...
     def items(self) -> list[tuple[str, _HeaderType]]: ...
-    def get(self, name: str, failobj: _T = ...) -> _HeaderType | _T: ...
-    def get_all(self, name: str, failobj: _T = ...) -> list[_HeaderType] | _T: ...
+    @overload
+    def get(self, name: str, failobj: None = None) -> _HeaderType | None: ...
+    @overload
+    def get(self, name: str, failobj: _T) -> _HeaderType | _T: ...
+    @overload
+    def get_all(self, name: str, failobj: None = None) -> list[_HeaderType] | None: ...
+    @overload
+    def get_all(self, name: str, failobj: _T) -> list[_HeaderType] | _T: ...
     def add_header(self, _name: str, _value: str, **_params: _ParamsType) -> None: ...
     def replace_header(self, _name: str, _value: _HeaderType) -> None: ...
     def get_content_type(self) -> str: ...
     def get_content_maintype(self) -> str: ...
     def get_content_subtype(self) -> str: ...
     def get_default_type(self) -> str: ...
     def set_default_type(self, ctype: str) -> None: ...
-    def get_params(self, failobj: _T = ..., header: str = "content-type", unquote: bool = True) -> list[tuple[str, str]] | _T: ...
-    def get_param(self, param: str, failobj: _T = ..., header: str = "content-type", unquote: bool = True) -> _T | _ParamType: ...
+    @overload
+    def get_params(
+        self, failobj: None = None, header: str = "content-type", unquote: bool = True
+    ) -> list[tuple[str, str]] | None: ...
+    @overload
+    def get_params(self, failobj: _T, header: str = "content-type", unquote: bool = True) -> list[tuple[str, str]] | _T: ...
+    @overload
+    def get_param(
+        self, param: str, failobj: None = None, header: str = "content-type", unquote: bool = True
+    ) -> _ParamType | None: ...
+    @overload
+    def get_param(self, param: str, failobj: _T, header: str = "content-type", unquote: bool = True) -> _ParamType | _T: ...
     def del_param(self, param: str, header: str = "content-type", requote: bool = True) -> None: ...
     def set_type(self, type: str, header: str = "Content-Type", requote: bool = True) -> None: ...
-    def get_filename(self, failobj: _T = ...) -> _T | str: ...
-    def get_boundary(self, failobj: _T = ...) -> _T | str: ...
+    @overload
+    def get_filename(self, failobj: None = None) -> str | None: ...
+    @overload
+    def get_filename(self, failobj: _T) -> str | _T: ...
+    @overload
+    def get_boundary(self, failobj: None = None) -> str | None: ...
+    @overload
+    def get_boundary(self, failobj: _T) -> str | _T: ...
     def set_boundary(self, boundary: str) -> None: ...
     @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]: ...
+    @overload
+    def get_charsets(self, failobj: None = None) -> list[str] | None: ...
+    @overload
+    def get_charsets(self, failobj: _T) -> list[str] | _T: ...
     def walk(self: Self) -> Generator[Self, None, None]: ...
     def get_content_disposition(self) -> str | None: ...
     def as_string(self, unixfrom: bool = False, maxheaderlen: int = 0, policy: Policy | None = None) -> str: ...