code: public String getSubjectName(String defaultName) {
          return (cert == null ? defaultName
                               : cert.getSubjectX500Principal().toString());
      }
docs: return string form of subject name from certificate associated with this
  build step, or a default name if no certificate associated with this
  build step, or if subject name could not be obtained from the
  certificate.
  
  @param defaultName name to use as default if unable to return a subject
  name from the certificate, or if no certificate.
  @returns String form of subject name or defaultName, if no certificate or
  if an exception was received while attempting to extract the subject name
  from the certificate.