Server crashes after displaying profile. Profile displays without avatar.

const fs = require("fs");

const mergeValues = (values, content) => {
  //cycle over all the keys
  for(var key in values) {
    content = content.replace("{{" + key + "}}", values[key]);
  }
    //replace all {{key}} with the value from the values object
  return content;
};

const view = (templateName, values, response) => {
  //read from the template files
  let fileContents = fs.readFileSync(`./views/${templateName}.html`, {encoding: "utf8"});
  //insert values into the content
  fileContents = mergeValues(values, fileContents);
  //write out the content
  response.write(fileContents);
};

module.exports.view = view;

const Profile = require("./profile.js");
const renderer = require("./renderer.js");
const querystring = require("querystring");

const commonHeader = {'Content-Type' : 'text/html'};

//Handle the HTTP route GET / and POST / i.e. Home
const home = (request, response) => {
  //if URL == "/" && GET
  if (request.url === "/") {
    if (request.method.toLowerCase() === "get") {
      //show search field
      response.writeHead('200', commonHeader);
      renderer.view('header', {}, response);
      renderer.view("search", {}, response);
      renderer.view("footer", {}, response);
      response.end();
    } else {
      //if URL == "/" && POST
        //get the post data
      request.on("data", (postBody) => {
        //extract from the data
        let query = querystring.parse(postBody.toString());
        //we need to redirect to localhost:8080/chalkers now
        response.writeHead(303, {"Location": "/" + query.username});
        response.end();
        //redirect to /:username
      });
    }
  }
};

//Handle the HTTP route GET /:username i.e. /chalkers or /tennysonhorn
const user = (request, response) => {
  //if URL == "/..."
  let username = request.url.replace("/", "");
  if (username.length > 0) {
    response.writeHead('200', commonHeader);
    renderer.view("header", {}, response);
    //get JSON from Treehouse
    let studentProfile = new Profile(username);
    //on "end"
    studentProfile.on("end", (profileJSON) => {
      //show profile

      //store the values we need
      let values = {
        avatarURL: profileJSON.gravatarURL,
        username: profileJSON.profile_name,
        badges: profileJSON.badges.length,
        javaScriptPoints: profileJSON.points.JavaScript,
      }
      //simple response
      renderer.view("profile", values, response);
      renderer.view("footer", {}, response);
      response.end();
    });

    //on "error"
    studentProfile.on("error", (error) => {
      //show error
      renderer.view("error", {errorMessage: error.message}, response);
      renderer.view("search", {}, response);
      renderer.view("footer", {}, response);
      response.end();
    });
  }
}

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