Working with NodeJS, Gulp, Jade: how can I use locals in my .jade files?

Question

So I'm trying to build a more or less simple web app with NodeJS, Express, Gulp and Jade for templating for the first time. I did not plan to use Gulp at first but after coding all the core functionalities I bought a template that came with Gulp. Without Gulp everything was running fine but I can't figure out how to make it work it with Gulp.

So here is my problem:

When I try to create my html files with gulp/gulp-jade I get the following error:

TypeError: /Users/root1/doordeals-be/views/admin-coupon-overview.jade:4
2|
3| block content
4|     h1 #{coupon.title}

Cannot read property 'title' of undefined

Here is how coupon is passed to jade in my Express route:

router.get('/:couponId', function(req, res, next) {
  Coupon.findById(req.params.couponId).populate('dispatch region').exec(function(err, coupon) {
    if(err) {
        return next(err);
    } else {
        res.render('admin-coupon-overview', {coupon: coupon});
    }
  });
});

Here is my gulp file:

gulp.task('serve', ['sass', 'templates'], function () {
browserSync.init({
    port: 3000,
    server: "./",
    index: './views/html/index.html',
    ghostMode: false,
    notify: false
});

gulp.watch('./src/assets/scss/**/*.scss', ['sass']);
gulp.watch('./src/**').on('change', browserSync.reload);

});

gulp.task('templates', function() {
  var YOUR_LOCALS = {};

gulp.src('./views/*.jade')
    .pipe(jade({
  locals: YOUR_LOCALS
  }))
  .pipe(gulp.dest('./views/html'))
});

That's basically it. So the problem is that coupon gets defined when someone sends a GET request to /:couponId (therefore he has to visit http://my.link.com/SOME-ID ) but Gulp tries to create all the HTML files as soon as the server gets started.

Does anyone know how to solve this issue?

Thanks in advance.