Returns container element type

    :param container_type:
    :param params:
    :return:

def container_elem_type(container_type, params):
    """
    Returns container element type

    :param container_type:
    :param params:
    :return:
    """
    elem_type = params[0] if params else None
    if elem_type is None:
        elem_type = container_type.ELEM_TYPE
    return elem_type