code: public ServiceFuture<CertificateBundle> mergeCertificateAsync(MergeCertificateRequest mergeCertificateRequest,
              final ServiceCallback<CertificateBundle> serviceCallback) {
          return mergeCertificateAsync(mergeCertificateRequest.vaultBaseUrl(), mergeCertificateRequest.certificateName(),
                  mergeCertificateRequest.x509Certificates(), mergeCertificateRequest.certificateAttributes(),
                  mergeCertificateRequest.tags(), serviceCallback);
      }
docs: Merges a certificate or a certificate chain with a key pair existing on the
  server.
  
  @param mergeCertificateRequest
  the grouped properties for merging a certificate request
  @param serviceCallback
  the async ServiceCallback to handle successful and failed
  responses.
  @return the {@link ServiceFuture} object