public static Map<String, Object> flattenKeysInMap(Map<String, Object> map, String separator) {
        Map<String, Object> answer = new LinkedHashMap<>();
        doFlattenKeysInMap(map, "", ObjectHelper.isNotEmpty(separator) ? separator : "", answer);
        return answer;
    }
@Test
    public void testflattenKeysInMap() {
        Map<String, Object> root = new LinkedHashMap<>();
        Map<String, Object> api = new LinkedHashMap<>();
        Map<String, Object> contact = new LinkedHashMap<>();
        contact.put("organization", "Apache Software Foundation");
        api.put("version", "1.0.0");
        api.put("title", "My cool API");
        api.put("contact", contact);
        root.put("api", api);
        root.put("cors", true);

        Map<String, Object> flattern = CollectionHelper.flattenKeysInMap(root, ".");
        assertEquals(4, flattern.size());
        assertEquals(true, flattern.get("cors"));
        assertEquals("1.0.0", flattern.get("api.version"));
        assertEquals("My cool API", flattern.get("api.title"));
        assertEquals("Apache Software Foundation", flattern.get("api.contact.organization"));
    }