Add None as possible parameter value to isnull/isna/notnull/notna (#325)

Author: gandhis1

pandas-stubs/core/dtypes/missing.pyi

@@ -30,7 +30,7 @@ def isna(obj: Index | list | ArrayLike) -> npt.NDArray[np.bool_]: ...
 @overload
 def isna(obj: Scalar) -> bool: ...
 @overload
-def isna(obj: NaTType | NAType) -> Literal[True]: ...
+def isna(obj: NaTType | NAType | None) -> Literal[True]: ...
 
 isnull = isna
 
@@ -43,6 +43,6 @@ def notna(obj: Index | list | ArrayLike) -> npt.NDArray[np.bool_]: ...
 @overload
 def notna(obj: Scalar) -> bool: ...
 @overload
-def notna(obj: NaTType | NAType) -> Literal[False]: ...
+def notna(obj: NaTType | NAType | None) -> Literal[False]: ...
 
 notnull = notna

tests/test_pandas.py

@@ -136,6 +136,9 @@ def test_isna() -> None:
     assert check(assert_type(pd.isna(pd.NaT), Literal[True]), bool)
     assert not check(assert_type(pd.notna(pd.NaT), Literal[False]), bool)
 
+    assert check(assert_type(pd.isna(None), Literal[True]), bool)
+    assert not check(assert_type(pd.notna(None), Literal[False]), bool)
+
     check(assert_type(pd.isna(2.5), bool), bool)
     check(assert_type(pd.notna(2.5), bool), bool)