code: public static X509Certificate getRootCert() {
  		if (null == rootCert) {
  			String path = SDKConfig.getConfig().getRootCertPath();
  			if (!isEmpty(path)) {
  				initRootCert();
  			} else {
  				LogUtil.writeErrorLog(SDKConfig.SDK_ROOTCERT_PATH + " not set in " + SDKConfig.FILE_NAME);
  				return null;
  			}
  		}
  		return rootCert;
  	}
docs: 从配置文件acp_sdk.properties中获取验签公钥使用的根证书
  @return