static public String map2String(final Map<String, String> tags) {
        if(tags != null && !tags.isEmpty()) {
            StringJoiner joined = new StringJoiner(",");
            for (Object o : tags.entrySet()) {
                Map.Entry pair = (Map.Entry) o;
                joined.add(pair.getKey() + "=" + pair.getValue());
            }
            return joined.toString();
        } else {
            return "";
        }
    }
@Test
    public void testMap2StringEmpty() {
        Map<String, String> map = new HashMap<>();
        Assert.assertEquals("", InfluxDbPoint.map2String(map));
    }