新注册商户没有证书，请问下这个开发指引中的httpClient能用公钥吗？如果可以的话怎么改，如果不可以的话有什么解决办法？谢谢
   private CloseableHttpClient httpClient;
    private CertificatesManager certificatesManager;
    private Verifier verifier;

    @Before
    //initialize verifier and build httpClient
    public void setup() throws GeneralSecurityException, IOException, HttpCodeException, NotFoundException {

        PrivateKey merchantPrivateKey = PemUtil.loadPrivateKey(privateKey);
        certificatesManager = CertificatesManager.getInstance();
        certificatesManager.putMerchant(merchantId, new WechatPay2Credentials(merchantId,
                        new PrivateKeySigner(merchantSerialNumber, merchantPrivateKey)),
                apiV3Key.getBytes(StandardCharsets.UTF_8));
        verifier = certificatesManager.getVerifier(merchantId);
        WechatPayHttpClientBuilder builder = WechatPayHttpClientBuilder.create()
                .withMerchant(merchantId, merchantSerialNumber, merchantPrivateKey)
                .withValidator(new WechatPay2Validator(verifier));
        httpClient = builder.build();
    }