private String serialise(final GraphQLResponse response) {

    if (response.getType() == GraphQLResponseType.NONE) {
      return EMPTY_RESPONSE;
    }

    return Json.encodePrettily(response.getResult());
  }
Returns the URL of the GraphQL HTTP service.

<p>This method constructs and returns the URL that the HTTP server is bound to. If the server
is not running, it returns an empty string.

@return the URL of the HTTP server, or an empty string if the server is not running.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/graphql/GraphQLHttpService.java