Why doesn't my model hook receive no param?

Disclaimer: major newbie warning!

I've successfully set up a Rails backend/Ember front-end project following this tutorial.

My router is

import Ember from 'ember';
import config from './config/environment';

var Router = Ember.Router.extend({
  location: config.locationType
});

Router.map(function() {
  this.resource('contacts', function() {
    this.resource('contact', { path: '/:contact_id' });
  });
});

export default Router;

Now I want to set up the possibility for finding only certain contacts based on the contact's lastName, so I followed the official docs for specifying query params.

I've modified my app/routes/contacts/index.js route so that it now looks like this:

import Ember from 'ember';

export default Ember.Route.extend({
  queryParams: {
    lastName: {
      refreshModel: true
    }
  },
  model: function(params) {
    return this.store.findQuery('contact', params);
  }
});

and app/controllers/contacts.js

import Ember from 'ember';

export default Ember.ArrayController.extend({

  queryParams: ['lastName'],
  lastName: null,

});

Unfortunately, params isn't filled, even when I specify a query param in the browser. More precisely, the params object looks like this:

which doesn't seem to contain anything interesting to me.

Yet, the query params information is somehow propagated to the view, so I feel slightly baffled. How can I have params be filled for the model hook in my route?