Backport PR #27664: BUG: added a check for if obj is instance of type in _isna-new (#27664) (#28041)

* added a check for if obj is instance of type in _isna-new

Author: TomAugspurger

doc/source/whatsnew/v0.25.1.rst

@@ -91,7 +91,7 @@ Indexing
 Missing
 ^^^^^^^
 
--
+- Bug in :func:`pandas.isnull` or :func:`pandas.isna` when the input is a type e.g. `type(pandas.Series())` (:issue:`27482`)
 -
 -
 

pandas/core/dtypes/missing.py

@@ -131,6 +131,8 @@ def _isna_new(obj):
     # hack (for now) because MI registers as ndarray
     elif isinstance(obj, ABCMultiIndex):
         raise NotImplementedError("isna is not defined for MultiIndex")
+    elif isinstance(obj, type):
+        return False
     elif isinstance(
         obj,
         (
@@ -169,6 +171,8 @@ def _isna_old(obj):
     # hack (for now) because MI registers as ndarray
     elif isinstance(obj, ABCMultiIndex):
         raise NotImplementedError("isna is not defined for MultiIndex")
+    elif isinstance(obj, type):
+        return False
     elif isinstance(obj, (ABCSeries, np.ndarray, ABCIndexClass)):
         return _isna_ndarraylike_old(obj)
     elif isinstance(obj, ABCGeneric):

pandas/tests/dtypes/test_missing.py

@@ -86,6 +86,10 @@ def test_isna_isnull(self, isna_f):
         assert not isna_f(np.inf)
         assert not isna_f(-np.inf)
 
+        # type
+        assert not isna_f(type(pd.Series()))
+        assert not isna_f(type(pd.DataFrame()))
+
         # series
         for s in [
             tm.makeFloatSeries(),