ember.js Sorting model in controller

ember.js version: 2.18.0

model:

export default DS.Model.extend({

  name: DS.attr('string'),
  description: DS.attr('string'),
  songs: DS.hasMany('song')
})

controller:

export default Controller.extend({
  sortBy: ['name:asc', 'description:asc'],
  sortedBands: computed.sort('model', 'sortBy')
}

ember gave me the following error:

Only string, number, symbol, boolean, null, undefined, and function are allowed as default properties ember/avoid-leaking-state-in-ember-objects