Python3 compliancy fix for GroupedItems

KCG/base/groupedelements.py

@@ -167,7 +167,7 @@ class GroupedObjects:
         :return: -
         """
         if group is None:
-            group = self._objects.keys()
+            group = list(self._objects.keys())
         groups = group if isinstance(group, list) else [group]
         items = item if isinstance(item, list) else [item]
         for gr in groups: