BUG: Fix isna cannot handle ambiguous typed list

Author: Licht-T

pandas/core/dtypes/missing.py

@@ -4,6 +4,7 @@
 import numpy as np
 from pandas._libs import lib, missing as libmissing
 from pandas._libs.tslib import NaT, iNaT
+from pandas.core.dtypes import cast
 from .generic import (ABCMultiIndex, ABCSeries,
                       ABCIndexClass, ABCGeneric,
                       ABCExtensionArray)
@@ -120,7 +121,9 @@ def _isna_new(obj):
         return _isna_ndarraylike(obj)
     elif isinstance(obj, ABCGeneric):
         return obj._constructor(obj._data.isna(func=isna))
-    elif isinstance(obj, list) or hasattr(obj, '__array__'):
+    elif isinstance(obj, list):
+        return _isna_ndarraylike(np.asarray(obj, dtype=object))
+    elif hasattr(obj, '__array__'):
         return _isna_ndarraylike(np.asarray(obj))
     else:
         return obj is None
@@ -202,6 +205,7 @@ def _isna_ndarraylike(obj):
 
         if is_string_like_dtype(dtype):
             # object array of strings
+            print('str')
             result = np.zeros(values.shape, dtype=bool)
         else:
             # object array of non-strings