def check_defaults(options, default):
    """Adds the values in default to options.

    Args:
        options (dict): base options.
        default (dict): default options.
    Returns:
        dict: options with the missing values that are in default but not in
        options.
    """
    if options is None:
        options = dict()
    if default is not None:
        for key, value in default.items():
            if key not in options:
                options[key] = value
    return options