code: public void delete(String name) throws CertificateException, IOException {
          if (name.equalsIgnoreCase(NOT_BEFORE)) {
              notBefore = null;
          } else if (name.equalsIgnoreCase(NOT_AFTER)) {
              notAfter = null;
          } else {
            throw new CertificateException("Attribute name not recognized by"
                             + " CertAttrSet:PrivateKeyUsage.");
          }
          encodeThis();
      }
docs: Delete the attribute value.
  @exception CertificateException on attribute handling errors.