@Override
    public HttpHeaders set(HttpHeaders headers) {
        if (headers instanceof DefaultHttpHeaders) {
            this.headers.set(((DefaultHttpHeaders) headers).headers);
            return this;
        } else {
            return super.set(headers);
        }
    }
@Test
    public void testSetNullHeaderValueValidate() {
        final HttpHeaders headers = new DefaultHttpHeaders(true);
        assertThrows(NullPointerException.class, new Executable() {
            @Override
            public void execute() {
                headers.set(of("test"), (CharSequence) null);
            }
        });
    }