code: public static String generateHash(String emailAddress) {
          if (StringUtils.isBlank(emailAddress)) {
              return null;
          }
          return DigestUtils.md5Hex(emailAddress.trim().toLowerCase()).toLowerCase();
      }
docs: Generates a hash value from the specified email address.
  Returns null if emailAddress is empty or null.
  @param emailAddress the email address to generate a hash from
  @return a hash value of the specified email address
  @since 1.0.0