mirage ember attributes are undefined

I'd like to use mirage with ember to simulate my api backend. I've followed the quick start and can get 10 entries via a call to the store:

return this.get('store').findAll('authors')

I've using createList to set this up, but when I view them only the id and type are correct. I can see the attribute names in ember chrome add on but everything is undefined.

Any idea what I'm doing wrong?

I thought it might be something to do with the serialiser which is:

import { JSONAPISerializer } from 'ember-cli-mirage';

export default JSONAPISerializer.extend({
});

I believe the attributes are normally in the data attribute and that is handled by ember data so it shouldn't need any further changes right?

Thanks!