'Updates a group.'

@infinisdk_to_cinder_exceptions
def update_group(self, context, group, add_volumes=None, remove_volumes=None):

    if (not vol_utils.is_group_a_cg_snapshot_type(group)):
        raise NotImplementedError()
    add_volumes = (add_volumes if add_volumes else [])
    remove_volumes = (remove_volumes if remove_volumes else [])
    infinidat_cg = self._get_infinidat_cg(group)
    for vol in add_volumes:
        infinidat_volume = self._get_infinidat_volume(vol)
        infinidat_cg.add_member(infinidat_volume)
    for vol in remove_volumes:
        infinidat_volume = self._get_infinidat_volume(vol)
        infinidat_cg.remove_member(infinidat_volume)
    return (None, None, None)
