def _Underride(d, **options):
    """Add key-value pairs to d only if key is not in d.

    If d is None, create a new dictionary.

    d: dictionary
    options: keyword args to add to d
    """
    if d is None:
        d = {}
    for key, val in options.items():
        d.setdefault(key, val)
    return d
