goog.net.XhrIo无法正常工作

I'm trying to use goog.net.XhrIo in the Closure library to do an Ajax call. Here's my code:

goog.require('goog.net.XhrIo');

function doRequest() {
    var request = new goog.net.XhrIo();

    goog.events.listen(request, goog.net.EventType.COMPLETE, function(){
      console.log("YES! YES! YES!");
    });
    request.send("http://some_url.com/update");
}
doRequest();

However, I'm getting this error:

TypeError: goog.structs.Map is not a constructor

I'm still a beginner at this so I have no idea what's up.