def string_is_bigger(s1, s2):
    """ Return s1 > s2 by taking into account None values.

    None is always smaller than any string.

    None > "string" works in python2 but not in python3. This function
    makes it work in python3 too.
    """
    if s1 is None:
        return False
    elif s2 is None:
        return True
    else:
        return s1 > s2