Get model defined in Meta.

    :param str or django.db.models.Model model:
    :return: model or None
    :rtype django.db.models.Model or None:
    :raise ValueError: model is not found or abstract

def get_concrete_model(model):
    """ Get model defined in Meta.

    :param str or django.db.models.Model model:
    :return: model or None
    :rtype django.db.models.Model or None:
    :raise ValueError: model is not found or abstract

    """
    if not(inspect.isclass(model) and issubclass(model, models.Model)):
        model = get_model_by_name(model)

    return model