EmberJS: Auto-Generate Record when no record ID in route

I am creating an application which lets applicants apply through a form. The form must auto-generate a new application if no previous application was passed in.

My router.js file:

Router.map(function () {
    this.route("apply", {path: ":application_id"}, function () {
        /* ... */
    });
});

And my routes/apply.js

export default Ember.Route.extend({

    model: function(params) {
        if (params["application_id"]) {
            console.dir(params.application_id);
            return this.store.find("application", params.application_id);
        }
        else {
            console.dir(params);
            let emptyApplicant = this.store.createRecord("applicant", {isPrimary: true}), emptyApplication = this.store.createRecord("application");
            emptyApplication.set("applicant", emptyApplicant);
            return emptyApplication;
        }
    }
});

But navigating to /apply gives me the following error:

Error while processing route: apply.index Couldn't find record of type 'application' for the id 'apply'. Error: Couldn't find record of type 'application' for the id 'apply'. at DS.LSAdapter.DS.Adapter.extend.find

I checked what the params is, and it is apply in this case (I was expecting it to be null, and the url apply/7g2c7 to be 7g2c7).

How can I detect when an application ID is being sent in, and auto-generate a new application otherwise?