/**
     *  Returns a string containing the string representation of each of {@code parts}, using the
     *  previously configured separator between each.
     * @param iterables 可遍历集合
     * @param separator 分隔符
     * @return
     */
    public static String convertToString(Iterable<?> iterables, String separator) {
        if(iterables == null) {
            return StringUtils.EMPTY;
        }
        return Joiner.on(separator).skipNulls().join(iterables);
    }