diff --git a/pandapower/io_utils.py b/pandapower/io_utils.py
index a24771a93..75434c4a3 100644
--- a/pandapower/io_utils.py
+++ b/pandapower/io_utils.py
@@ -575,14 +575,16 @@ def DataFrame(self):
                 if column_names is not None:
                     df.columns.names = column_names
 
-        # recreate jsoned objects
-        for col in ('object', 'controller'):  # "controller" for backwards compatibility
-            if (col in df.columns):
-                df[col] = df[col].apply(partial(
-                    self.pp_hook, ignore_unknown_objects=self.ignore_unknown_objects
-                ))
         if 'geo' in df.columns:
             df['geo'] = df['geo'].dropna().apply(json.dumps).apply(geojson.loads)
+
+        df_obj = df.select_dtypes(include=['object'])
+        for col in df_obj:
+            df[col] = df[col].apply(partial(
+                self.pp_hook, ignore_unknown_objects=self.ignore_unknown_objects
+            ))
+            df[col] = df[col].astype(dtype = 'object')
+            df.loc[pd.isnull(df[col]), col] = None
         return df
 
     @from_serializable.register(class_name='pandapowerNet', module_name='pandapower.auxiliary')#,