/**
  * Add a response for a particular Certificate ID.
  *
  * @param certID certificate ID details
  * @param certStatus status of the certificate - null if okay
  */
 public void AddResponse(
     CertificateID certID,
     CertificateStatus certStatus)
 {
     list.Add(new ResponseObject(certID, certStatus, DateTime.UtcNow, null));
 }