Unable to display web page due to undefined property 'url'

treehouse:~/workspace$ node app.js                                                                          
Server running at http://<workspace-url>/                                                                   
/home/treehouse/workspace/router.js:21                                                                      
        var username = request.url.replace("/","");                                                         
                              ^                                                                             

TypeError: Cannot read property 'url' of undefined                                                          
    at Object.user (/home/treehouse/workspace/router.js:21:24)                                              
    at Server.<anonymous> (/home/treehouse/workspace/app.js:10:9)                                           
    at emitTwo (events.js:87:13)                                                                            
    at Server.emit (events.js:172:7)                                                                        
    at HTTPParser.parserOnIncoming [as onIncoming] (_http_server.js:528:12)                                 
    at HTTPParser.parserOnHeadersComplete (_http_common.js:88:23)  

var Profile = require("./profile.js");
var studentProfile = new Profile("chalkers");


//Handle HTTP route GET / and POST / i.e. Home
function home(request,response) {
    //if the URL == "/" && GET 
    //show the search field
    if(request.url ==="/"){
    response.writeHead(200, {'Content-Type': 'text/plain'});
    response.write("Header\n");
    response.write("Search\n");
    response.end("Footer\n");
    }
  //if url =="/" && POST 
    //redirect to /:username
}

//Handle the HTTP route GET /:username i.e.  /ericpark
function user(request, response) {
    var username = request.url.replace("/","");
    if(username.length > 0) {
        response.writeHead(200, {'Content-Type': 'text/plain'});
        response.write("Header\n");

        //Get JSON from Treehouse
        var studentProfile = new Profile(username);
        //On "End"
        studentProfile.on("end", function(profileJSON){
            //Show profile
            //Store the values which we need
            var values = {
                avatarUrl: profileJSON.gravatar_url,
                username: profileJSON.profile_name,
                badges: profileJSON.badges.length,
                javascriptPoints:profileJSON.points.JavaScript
            }
            //Simple reponse
            response.write(values.username+"\n");
            response.end('Footer\n');
        });

        //on "end"
        //show profile 
      //on "error"
        studentProfile.on("error", function(error){
        reponse.write(error.message + "\n");
            response.write(username+"\n");
            response.end('Footer\n');
        });
    }
}
    //if url =="/...." 
    //get json from Treehouse 


module.exports.home = home;
module.exports.user = user;