What is wrong with this restify client code?

Question

I have a server URL like this;

http://127.0.0.1:8888/stk?list=XXX,YYY

The server URL is tested to be working. I have a restify client that makes a HTTP GET to this URL and if things are working, a json output will be returned.

This is how the restify client code looks like;

var restify = require('restify');

var client = restify.createClient({
    url: 'http://127.0.0.1:8888'
});

    client.get('/stk?list=XXX,YYY', function(err, req) {
        assert.ifError(err); // connection error

        req.on('result', function(err, res) {
            assert.ifError(err); // HTTP status code >= 400
            res.body = '';
            res.setEncoding('utf8');
            res.on('data', function(chunk) {
                res.body += chunk;
            });

            res.on('end', function() {
                console.log(res.body);
            });
        });
    });

The error was at assert.ifError(err); because err was null.

What is wrong with the code?