JSONSerializer EmberJS is not accepting expected format

Based on the documentation here: http://ift.tt/1WGabbV JSONSerializer is the right serializer for me to use for my API.

Despite that I receive the following error:

ember.debug.js:28535 Error while processing route: core.admin.users Cannot read property 'type' of undefined TypeError: Cannot read property 'type' of undefined

The API response looks like this:

{
    "errors": [],
    "data": [
        {
            "first_name": "Foo",
            "last_name": "Bar"
        },
        {
            "first_name": "Moo",
            "last_name": "Boo"
        }
    ],
    "version": 1
}

My Model looks like so:

import Model from 'ember-data/model';
import attr from 'ember-data/attr';

export default Model.extend({
    first_name: attr('string'),
    last_name: attr('string')

});

My Application Adapter:

import RESTAdapter from 'ember-data/adapters/rest';

export default RESTAdapter.extend({
  headers:  {
      'Accepts': 'application/json',
      'Accept': 'application/json'
    }
});

My User Adapter:

import ApplicationAdapter from './application';

export default ApplicationAdapter.extend({
    buildURL: function(){
        return 'core/users/foobar';
    }
});

And finally my application Serializer:

import JSONSerializer from 'ember-data/serializers/json';

export default JSONSerializer.extend({
});