BUG: CategoricalIndex.get_indexer issue with NaNs (pandas-dev#45361)

Update: Replaced `np.isnan` with `pandas.core.dtypes.missing.isna`

Author: Shashank-Shet

pandas/core/indexes/base.py

@@ -3700,8 +3700,8 @@ def get_indexer(
         # belong to some category are changed to NaNs
         # Mask to track actual NaN values compared to inserted NaN values
         try:
-            target_nans = np.isnan(target)
-        except TypeError as e:
+            target_nans = isna(target)
+        except NotImplementedError:
             target_nans = False
         target = self._maybe_cast_listlike_indexer(target)