assertTrue(docMap.containsValue("value1"));
        assertTrue(docMap.containsValue(null));
        assertFalse(docMap.containsValue("nonexistent"));
    }

    public void test_null_values() {
        Map<String, Object> parentMap = new HashMap<>();
        DocMap docMap = new DocMap(parentMap);

        docMap.put("nullKey", null);
        assertTrue(docMap.containsKey("nullKey"));