right.js

Property.findOne({ 
  _id: propertyId 
}).then(function (property) {
  var reservation = new Reservation({
    message: req.body.message,
    property: propertyId,
    guest: user.id
  });

  return reservation.save();
}).then(function () {
  notifier.sendNotification();
  res.redirect('/properties');
}).catch(function(err) {
  console.log(err);
});

wrong.js

Property.findOne({ _id: propertyId })
.then(function (property) {
  var reservation = new Reservation({
    message: req.body.message,
    property: propertyId,
    guest: user.id
  });

  return reservation.save();
})
.then(function () {
  notifier.sendNotification();
  res.redirect('/properties');
})
.catch(function(err) {
  console.log(err);
});