def seconds_to_hhmmss(seconds):
    """Parses the number of seconds after midnight and returns the corresponding HH:MM:SS-string.

    Args:
        seconds (float): number of seconds after midnight.

    Returns:
        str: the corresponding HH:MM:SS-string.
    """
    if seconds is None:
        return None
    int_seconds = int(seconds)
    m, s = divmod(int_seconds, 60)
    h, m = divmod(m, 60)
    return "{:02d}:{:02d}:{:02d}".format(h, m, s)