def check_annulus(args):
    """
    Checks and formats the annulus values.

    :param args: The command-line arguments.

    :type args: argparse.ArgumentParser Namespace

    :returns: argparse.ArgumentParser Namespace -- The updated command-line
        arguments.
    """
    if not (args.annulus1 and args.annulus2) and not args.annulus:
        args.annulus = None
    elif args.annulus1 and args.annulus2:
        args.annulus = [args.annulus1, args.annulus2]
    else:
        args.annulus = list(args.annulus)
        if not (args.annulus1 and args.annulus2):
            args.annulus1 = args.annulus[0]
            args.annulus2 = args.annulus[1]
    return args
