@Override
    public HttpHeaders add(HttpHeaders headers) {
        if (headers instanceof DefaultHttpHeaders) {
            this.headers.add(((DefaultHttpHeaders) headers).headers);
            return this;
        } else {
            return super.add(headers);
        }
    }
@Test
    public void addIterable() {
        final DefaultHttpHeaders headers = newDefaultDefaultHttpHeaders();
        headers.add(HEADER_NAME, HeaderValue.THREE.asList());
        assertDefaultValues(headers, HeaderValue.THREE);
    }