def validate_key_values(config_handle, section, key, default=None):
    """Warn when *key* is missing from configuration *section*.

    Args:
        config_handle (configparser.ConfigParser): Instance of configurations.
        section (str): Name of configuration section to retrieve.
        key (str): Configuration key to look up.
        default (object): Default object to use when *key* is not found.

    Returns:
        object: ``str`` when *key* exists, otherwise *default* object.
    """
    if section not in config_handle:
        LOG.info('Section missing from configurations: [%s]', section)

    try:
        value = config_handle[section][key]
    except KeyError:
        LOG.warning('[%s] missing key "%s", using %r.', section, key, default)
        value = default

    return value