def get_sub_model(model_object):
    """Return the model inherited sub class instance.

    Used as a workaround for Django subclasses issues

    Args:
        model_object (django.models.Model): model instance.

    Returns:
        object: sub model instance. None if there is no sub model.
    """
    for sub_class in model_object.__class__.__subclasses__():
        possible_atter = sub_class.__name__.lower()

        if hasattr(model_object, possible_atter):
            sub_model = getattr(model_object, possible_atter)
            sub_sub_model = get_sub_model(sub_model)

            if sub_sub_model is not None:
                return sub_sub_model

            return sub_model

    return None