expressjs get request error 500

So I recently started working with expressjs. now i have a problem with my routing in get requests. this is my app.js:

    var express = require('express');
    var path = require('path');
    var favicon = require('serve-favicon');
    var logger = require('morgan');
    var cookieParser = require('cookie-parser');
    var bodyParser = require('body-parser');
    var session = require('express-session');
    app.use(logger('dev'));
    app.use(bodyParser.json());
    app.use(bodyParser.urlencoded({ extended: false }));
    app.use(cookieParser());
    app.use(express.static(path.join(__dirname, 'public')));
    var login=require('./routes/login');//get a js file login.js
    app.use('/user_form',login);

in the loginjs i have two requests:

 var express = require('express');
 var router = express.Router();
 var bodyparser = require("body-parser");
 var urlencodedParser = bodyparser.urlencoded({ extended: false });

    router.post("/", function (req,res,next) {
    var sess = req.session;
    var answer = {
        username: req.body.username,
        password: req.body.password
    };
    if (users[answer.username] && users[answer.username].password == 
    answer.password) {
        users[answer.username].logged = true;
        sess.logged = answer.username;
        res.redirect("/");
    }
    else {
        res.render("fail");
    }
    });

    router.get("/logged", function (req, res) {
    sess = req.session;
    res.send(sess.logged);
    });

the post one works but the get one doesn't , it always gives me error 500 and i cannot figure out the problem.

this is the code in the client side :

   $.ajax({
    type: "GET",
    url: "user_form/logged",
    dataType: "xml"
  }).done(function (res) {
   alert(res);
  }).fail(function (jqXHR, textStatus, errorThrown) {
    alert("AJAX call failed: " + textStatus + ", " + errorThrown);
  });

any help appreciated !

via Nir Tshuva