class CollectionUtils {

    public static Map<String, List<String>> joinAll(Map<String, Map<String, String>> map, String separator) {
        if (map == null) {
            return null;
        }
        Map<String, List<String>> result = new HashMap<String, List<String>>();
        for (Map.Entry<String, Map<String, String>> entry : map.entrySet()) {
            result.put(entry.getKey(), join(entry.getValue(), separator));
        }
        return result;
    }

    private  CollectionUtils();

}