express 使用passport 出现 passport.initialize() middleware not in use错误

   app.get("/login/github", passport.authenticate("github", {session: false}));
app.get("/login/github/callback", passport.authenticate("github", {
      session: false,
      failureRedirect: '/login',
      successFlash: '登陆成功！'
}), function (req, res) {
      req.session.user = {name: req.user.username, head: "https://gravatar.com/avatar/" + req.user._json.gravatar_id + "?s=48"};
     res.redirect('/');
});

app.js里面也添加了:

    app.use(passport.initialize());
    passport.use(new GithubStrategy({
      clientID: "xxx",
      clientSecret: "xxx",
      callbackURL: "xxx"
   }, function(accessToken, refreshToken, profile, done) {
       done(null, profile);
  }));