code: public void set(String name, Object obj) throws IOException {
          if (!(obj instanceof SerialNumber)) {
              throw new IOException("Attribute must be of type SerialNumber.");
          }
          if (name.equalsIgnoreCase(NUMBER)) {
              serial = (SerialNumber)obj;
          } else {
              throw new IOException("Attribute name not recognized by " +
                                  "CertAttrSet:CertificateSerialNumber.");
          }
      }
docs: Set the attribute value.