def get_available_group(car):
    """
    Detect and, if is possible, assign a group to a car

    :param car: Available car that wants a group
    :type car: journey.Car

    :returns: Group assigned if is possible, None if isn't
    :type returns: journey.Group
    """
    group = car.get_available_group()
    if group:
        group.assign_car(car)
    return group