def read_config(config, section, item):
    """ Get the string value of a config item, returning None if the value        is "None"

    :param config: The configuration to look things up in.
    :param section: The section name
    :type section: str
    :param item: The item name.
    :type item: str
    :rtype: str or None
    """
    value = config.get(section, item)
    if value == 'None':
        return None
    return value
