Why I get user and not users on users/index route?

I tried to make a simple emberapp with rails, that shows some users info from our system.

My route: /api/users returns this json:

{"users":[{"id":1,"username":"Evolutio","email":"mail@evolutio.tld"}]}

My emberadapter:

import DS from 'ember-data';
export default DS.RESTAdapter.extend({
    host: 'https://api.domain.tld',
    namespace: 'api',
    headers: {
        //"API_KEY": "secret key",
    }
});

my users/model.js

import DS from 'ember-data';

export default DS.Model.extend({
  username: DS.attr('string'),
  email: DS.attr('string')
});

my users/index/route.js

import Ember from 'ember';

export default Ember.Route.extend({
    model() {
        let users = this.store.findAll("users");
        return users;
    }
});

I visit this url: localhost:4200/users

When I delete the user/model.js I get this error:

WARNING: Encountered "users" in payload, but no model was found for model name "user" (resolved model name using frontend@serializer:application:.modelNameFromPayloadKey("users"))

and the data with the ember inspector: