code: private boolean validCharacters(String value) {
          if (INVALID_CHARACTERS.contains(value)) {
              LOG.error("Flash key or value can not contain the following characters: spaces, |, & or :");
              return false;
          }
  
          return true;
      }
docs: Checks if the given value contains characters that are not allowed
  in the key or value of a flash cookie
  
  @param value The value to check
  @return True if the given string is valid, false otherwise