You cannot add or remove an unsaved Parse Object from a relation

Question

I'm trying to add relation between my Place & User classes. But getting "You cannot add or remove an unsaved Parse Object from a relation" error. My code is like below.

var user = req.session.user;
var placeId = req.body.placeId;

var placeQuery = new Parse.Query('Place');
placeQuery.equalTo('objectId', placeId);
placeQuery.first()
.then(function (place) {
  place.increment('likeCount');
  var relation = place.relation('likes');
  relation.add(user);
  return place.save(null, {useMasterKey : true})
})
.then(function () {
  return next();
})
.then(function (error) {
  return res.status(500).send(error);
})