fixing broken tests for legacy lightsim2grid

Author: BDonnot

grid2op/Space/GridObjects.py

@@ -1610,19 +1610,22 @@ def _fill_names(cls):
             cls._reset_cls_dict()
 
         if cls.shunts_data_available and cls.name_shunt is None:
-            cls.name_shunt = [
-                "shunt_{}_{}".format(bus_id, sh_id)
-                for sh_id, bus_id in enumerate(cls.shunt_to_subid)
-            ]
-            cls.name_shunt = np.array(cls.name_shunt)
-            warnings.warn(
-                "name_shunt is None so default storage unit names have been assigned to your grid. "
-                "(FYI: storage names are used to make the correspondence between the chronics and "
-                "the backend)"
-                "This might result in impossibility to load data."
-                '\n\tIf "env.make" properly worked, you can safely ignore this warning.'
-            )
-            cls._reset_cls_dict()
+            if cls.shunt_to_subid is not None:
+                # used for legacy lightsim2grid
+                # shunt names were defined after...
+                cls.name_shunt = [
+                    "shunt_{}_{}".format(bus_id, sh_id)
+                    for sh_id, bus_id in enumerate(cls.shunt_to_subid)
+                ]
+                cls.name_shunt = np.array(cls.name_shunt)
+                warnings.warn(
+                    "name_shunt is None so default shunt names have been assigned to your grid. "
+                    "(FYI: shunt names are used to make the correspondence between the chronics and "
+                    "the backend)"
+                    "This might result in impossibility to load data."
+                    '\n\tIf "env.make" properly worked, you can safely ignore this warning.'
+                )
+                cls._reset_cls_dict()
 
     @classmethod
     def _check_names(cls):