Need help getting restapi to work

I'm trying to use the restapi.js to fetch a user from my rest service. I successfully am making a request but after that I'm getting the error:

"'null' is not an object (evaluating 'item[model.idAttribute]')";

from the restapi.js.

My Model:

exports.definition = {  
    config: {
        URL: "http://192.168.178.40/api/user",
        //"debug": 1, 
        "adapter": {
            type: "restapi",
            collection_name: "users",
            idAttribute: "id"
        }
    },      
    extendModel: function(Model) {      
        _.extend(Model.prototype, {
        });
        return Model;
    },  
    extendCollection: function(Collection) {        
        _.extend(Collection.prototype, {
        });
        return Collection;
    }       
};

The json response from the request (captured by a network tool):

{"id":1237385,"UserName":"klaasje","UserType":1,"PictureType":2,"PicturePath":"/userimages/401/0_5b7abd22-93ca-4321-be45-cfa8f18cf396_thumb.JPG","PublicUrl":null,"Status":1,"Email":"elger@dp.com","Password":"bla","StatusChanged":"2014-02-20T14:17:05","BirthDate":"1994-01-01T00:00:00","TopicID":79399,"IsFemale":false,"Age":20}

The way the request is made:

// get user
var model = Alloy.createModel('user',{id: 1237385});
 
 //the fetch method is an async call to the remote REST API. 
model.fetch({ 
    success : function(){
 
    },
    error : function(){
        Ti.API.error("hmm - this is not good!");
    }
});

And finally this error:

[ERROR] :  Script Error {
[ERROR] :      backtrace = "#0 () at file:///Users/elgerm/Library/Application%20Support/iPhone%20Simulator/7.0.3/Applications/6ECCA5FA-C952-4B9D-A36A-A5239FDCE5F4/soichat.app/alloy/sync/restapi.js:34";
[ERROR] :      line = 133;
[ERROR] :      message = "'null' is not an object (evaluating 'item[model.idAttribute]')";
[ERROR] :      name = TypeError;
[ERROR] :      sourceId = 334709920;
[ERROR] :      sourceURL = "file:///Users/elgerm/Library/Application%20Support/iPhone%20Simulator/7.0.3/Applications/6ECCA5FA-C952-4B9D-A36A-A5239FDCE5F4/soichat.app/alloy/sync/restapi.js";
[ERROR] :  }

What am I doing wrong? Am I missing something?