Passing an array to a rendered page (Async?)

I'm trying to display an array via the jade view engine after fetching data from mongodb with a mongoose scheme unfortunately the array doesn't reach the user due to an error code 500 recieved when adressing the page , I think this happens due to a timing issue (the page gets rendered before the code has a chanse to get the data) because the data is present in the code and i am able to log it to the console however the error code appears in the console prior to the data being logged ... does anyone have an idea of how I can resolve this issue ?

---

The node code:

let validateUserToSession = function(req,res,next){
let PlayLst=[];
if(req.session && req.session.user)
 {
   Schemes.User.findOne({eMail:req.session.user.eMail},function(err,user) {
     if(!user)
     {
       req.session.reset();
       res.render('login',{message:{error:'Please log in ...',status:0}})
     }
     else
     {
       PlayLst=[];
       Schemes.PlayList.findOne({ref:user.id},function(err,playlist) {
         if(err)
          {PlayLst=['No Tracks were chosen...']}
          else{
            if(playlist!==null){  
            playlist.favSongs.forEach(function(element) {
              PlayLst.push(element.Artist + " " + element.Track);
              console.log(PlayLst);
            });   
          }}})

          res.locals.PlayLst = PlayLst;
          res.locals.user=user;
          res.render('index',{ title: 'Index' });              
     }
   });
 }
else{
  res.render('login',{message:{error:'Please log in ...',status:0}})
 }
}

/* GET home page and preform validation on user */
router.get('/index',validateUserToSession);

---

Pug (Jade...) code :

  h2 Logged in as : #{session.user.nName}
  p Name: #{session.user.fName} #{session.user.lName}
  p E-Mail: #{session.user.eMail}
  if (session.PlayLst.length != undefined && session.PlayLst.length>0)
  ul Favorite Songs : 
   each track in session.PlayLst
    li = track

---

Client Side Error:

\index.jade:21 19| p Name: #{session.user.fName} #{session.user.lName} 20| p 
E-Mail: #{session.user.eMail} > 21| if (session.PlayLst.length != undefined 
&& session.PlayLst.length>0) 22| ul Favorite Songs : 23| each track in 
session.PlayLst 24| li = track Cannot read property 'length' of undefined

  TypeError: C:\SomePath\index.jade:21
  19|    p Name: #{session.user.fName} #{session.user.lName}
  20|    p E-Mail: #{session.user.eMail}
> 21|    if (session.PlayLst.length != undefined && session.PlayLst.length>0)
  22|    ul Favorite Songs : 
  23|     each track in session.PlayLst
  24|      li = track

---

Console Error Image

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via Gal Ratzkin