@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 testAsciiStringKeyRetrievedAsString() {
        final HttpHeaders headers = new DefaultHttpHeaders(false);

        // Test adding AsciiString key and retrieving it using a String key
        final String cacheControl = "no-cache";
        headers.add(HttpHeaderNames.CACHE_CONTROL, cacheControl);

        final String value = headers.getAsString(HttpHeaderNames.CACHE_CONTROL);
        assertNotNull(value);
        assertEquals(cacheControl, value);

        final String value2 = headers.getAsString(HttpHeaderNames.CACHE_CONTROL.toString());
        assertNotNull(value2);
        assertEquals(cacheControl, value2);
    }