code: public String getURN() throws InvalidRegistrationContentException {
          if (parsedConfig==null || parsedConfig.urn==null || parsedConfig.urn.trim().isEmpty()) {
              throw new InvalidRegistrationContentException("Invalid registration config - failed to read mediator URN");
          }
          return parsedConfig.urn;
      }
docs: Reads and returns the mediator URN from the JSON content.
  
  @see #RegistrationConfig(String)