switch to RESTAdapter - EmberJS

I have been looking at EmberJS tutorials, but all of them use FixtureAdapter, and I'm trying to switch to RESTAdapter, but I'm facing a persistent error

Error: Assertion Failed: Expected an object as `data` in a call to push for Books.Book , but was undefined

here's the code for the adapter:

Books.ApplicationAdapter = DS.RESTAdapter.extend({
host: 'http://localhost:24818/api/'});

and calling the api in the router:

Books.BooksRoute = Ember.Route.extend({
model: function() {
return this.store.find('book',1);
 } 
});

How do I get store.find to return a JSON to be used in the Handlebars template?

Many thanks,

Edit: this is my API response:

[{"Id":1,"Title":"Pride and Prejudice","Year":1813,"Price":9.99,"Genre":"Comedy of manners","AuthorId":1,"Author":null},{"Id":2,"Title":"Northanger Abbey","Year":1817,"Price":12.95,"Genre":"Gothic parody","AuthorId":1,"Author":null},{"Id":3,"Title":"David Copperfield","Year":1850,"Price":15.00,"Genre":"Bildungsroman","AuthorId":2,"Author":null},{"Id":4,"Title":"Don Quixote","Year":1617,"Price":8.95,"Genre":"Picaresque","AuthorId":3,"Author":null}]