Update _check.py

sktime/datatypes/_series/_check.py

@@ -67,7 +67,7 @@ def check_pddataframe_series(obj, return_metadata=False, var_name="obj"):
     # pd.DataFrame mtype allows object dtype,
     # but if we allow object dtype with pd.Series entries,
     # the mtype becomes ambiguous, i.e., non-delineable from nested_univ
-    if len(obj) > 0 and isinstance(obj.iloc[0, 0], (pd.Series, pd.DataFrame)):
+    if np.prod(obj.shape) > 0 and isinstance(obj.iloc[0, 0], (pd.Series, pd.DataFrame)):
         msg = f"{var_name} cannot contain nested pd.Series or pd.DataFrame"
         return ret(False, msg, None, return_metadata)