code: public SerialNumber getSerialNumberObject() {
          if (info == null)
              return null;
          try {
              SerialNumber ser = (SerialNumber)info.get(
                                CertificateSerialNumber.NAME + DOT +
                                CertificateSerialNumber.NUMBER);
             return ser;
          } catch (Exception e) {
              return null;
          }
      }
docs: Gets the serial number from the certificate as
  a SerialNumber object.
  
  @return the serial number.