Field is not computed when model is created with an empty hash

[blikblum]

Tested with backbone 1.1.2
In the example below, m.get('test') returns undefined
http://jsfiddle.net/N4zh4/1/
if i create the model with var m = new MyModel({x: 2}); it works

var MyModel = Backbone.Model.extend({

initialize: function () {
    this.computedFields = new Backbone.ComputedFields(this);
},
computed: {
    test: {
        get: function () {
            console.log('get');
            return 5;                
        }            
    }        
 }    
});
var m = new MyModel({});
console.log(m.get('test'));