Must override the DS.FixtureAdapter::queryFixtures method to support querying the fixture store

I'm trying to set this up so that I can query my fixtures, but I get the above error. In app.js, I have:

App.ApplicationAdapter = DS.FixtureAdapter;

Here's my model method for the index route:

model: function(params) {

    /* pagination */
    var page;

    if(params.page){
      page = params.page;
      // avoid page numbers to be trolled i.e.: page=string, page=-1, page=1.23
      page = isNaN(page) ? 1 : Math.floor(Math.abs(page));
      // page=1 will result into offset 0, page=2 will result into offset 10 and so on
      this.set('offset', (page-1)*this.get('limit'));
    }

    return Ember.RSVP.hash({
        users: this.store.find('user'),
        topics: this.store.find('topic', {
            offset: this.get('offset'),
            limit: this.get('limit')
        })
    });
}

And the topic.js model:

import DS from 'ember-data';

var Topic = DS.Model.extend({
  title:            DS.attr('string'),
  icon:             DS.attr('string'),
  color:            DS.attr('string'),

  discussions:      DS.hasMany('discussion', {async: true})
});

Topic.reopenClass({
    FIXTURES: [
        {
            id: 1,
            title: "This House would ban beauty contests",
            color: "#2ecc71",
            discussions: [1, 2]
        },
        {
            id: 2,
            title: "This House would make physical education compulsory",
            color: "#e74c3c",
            discussions: [3, 4]
        },
        {
            id: 3,
            title: "This House would allow prisoners to vote",
            color: "#e74c3c",
            discussions: [5, 6]
        }
    ]
});

Topic.reopenClass({
    queryFixtures: function(fixtures, query){
        var properties;

        properties = Object.keys(query);

        // adding pagination support
        if(properties.contains('offset')){
          fixtures = fixtures.slice(query.offset, query.offset+query.limit);
        }

        return fixtures;
    }
})

export default Topic;

What am I doing wrong here?