Ember: setting controller properties in init()?

Having a hard time figuring out why controller properties added in init() are added as 'undefined' rather than with default values. I guess you're supposed to do define in init() to avoid "leaking state"? I think I am missing something fundamental here.

When a controller property like an empty array is specified right on the controller it's added as 'Array[0]', which then allows you to pushObject stuff into it. When added in init() they are added as 'undefined' so pushObject fails.

See demo on this twiddle and/or the code below:

import Ember from 'ember';

export default Ember.Controller.extend({

    queryParams: ['q','sort_method','search_type','filter1','filter2'],

    init(){
        this._super(...arguments);

        Ember.set(this, 'q', null);
        Ember.set(this, 'sort_method', 'relevance'); // <-- sets default value to 'undefined'
        Ember.set(this, 'filter1', []); // <-- sets default value to 'undefined'
    },

  filter2: [], // <-- sets default values properly but will it cause state issues?
  search_type: 'bar'

});

Basically, I'm wanting to figure out how to declare my list of query params in ONE place (like in config file), rather than 3 places (route, controller queryParams array, and to the controller itself)

I created a twiddle to illustrate what I mean.