private void handleGraphQLError(final RoutingContext routingContext, final Exception ex) {
    LOG.debug("Error handling GraphQL request", ex);
    final HttpServerResponse response = routingContext.response();
    if (!response.closed()) {
      response
          .setStatusCode(HttpResponseStatus.BAD_REQUEST.code())
          .end(Json.encode(new GraphQLErrorResponse(ex.getMessage())));
    }
  }
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