pug : TypeError: View is not a constructor

I'm trying to make a website using NodeJS with express and pug for templates. I integrated Pug using the express docs, but I keep getting TypeError: View is not a constructor on the render function. I really looked, but the only people who had this problem got it with other templates, and were not doing it has simple. So at the end I did it like this :

var express = require('express');
var server = express();

server.set('views', './views');
server.set('view engine', 'pug');

server.get('/', (req, res) => {
  res.render('example', {title: "code", message: "message"});
});
...

server.listen(server.settings.port);
console.log('Server listening on port', server.settings.port);

And in views/ the template looks like :

html
  head
    title = title
  body
    h1 = message

In package.json, I imported it like : "pug": "^2.0.0-rc.1"

Thank you for your tips ! And have a nice day.

via CodingMouse