def serialize_m2m_on_save(sender, action, instance, using, **kwargs):
    """ Part of the serialize transaction process that ensures m2m are
    serialized correctly.

    Skip those not registered.
    """
    if action == "post_add":
        try:
            wrapped_instance = site_offline_models.get_wrapped_instance(instance)
        except ModelNotRegistered:
            pass
        else:
            wrapped_instance.to_outgoing_transaction(using, created=True)