Bakbone RelationalModel Bug

I need help on a bug when fetching submodel with RelationalModel for Backbone.js

HTML

<script src="http://underscorejs.org/underscore-min.js"></script>
<script src="http://backbonejs.org/backbone-min.js"></script>
<script src="http://manager.boap.net/lib/backbone.relational.js"></script>
<div id="foo"></div>

<script type="text/template" id="tpl-foo">
<%
    products.each(function(value, index) {
        %>
            <h1>Product number [<%= index %>] :</h1>
            <div id="object">
                <%= JSON.stringify(value).replace(/,/g , ",<br />") %>
            </div>
            <div id="userid">
                user_id value : <%= value.get('user_id') %>
            </div>
        <%
    });
%>
</script>

CSS

#object {
    border:1px dashed red;
    font-family:"courier new";
    padding:10px;
}

#userid {
    border:1px dashed green;
    font-family:"courier new";
    padding:10px;
    margin-top:10px;
}

JavaScript

$(function(){
    // User Model
    var User = Backbone.RelationalModel.extend(
    {
    
        urlRoot: 'http://noraj.fr:5000/users',
        defaults: {
            id: '',
            name: '',
            email: '',
            firstname: '',
            lastname: '',
            password: '',
            card_nb: '',
            cart_total: ''
        }
    
    });
    // Product Model
    var Product = Backbone.RelationalModel.extend(
    {
    
        urlRoot: 'http://noraj.fr:5000/products',
        defaults: {
            id: '',
            name: '',
            description: '',
            current_price: '',
            categories: '',
            duration: '',
            shipping_cost: '',
            start_date: '',
            is_buy_it_now: '',
            user_id: null
        },
    
        relations: [{
            type: Backbone.HasOne,
            key: 'user_id',
            autoFetch: true,
            relatedModel: User
        }]
    
    });
    
    // Products (collection of Product Models)
    var Products = Backbone.Collection.extend(
    {
        model: Product,
        url: 'http://noraj.fr:5000/products'
    
    });
    
    var ProductListView = Backbone.View.extend({
        initialize: function () {
        },
    
        render: function () {
            var products = 0;
            var el = this.el;
    
            Backbone.Relational.showWarnings = true;
            products = new Products();
            products.fetch({
                success: function() {
                    $("#foo").html(_.template($("#tpl-foo").html(),{products:products}));
                },
                error: function() {
                    //app.navigate("/", true);
                }
            });
        }
    });
    var App = new ProductListView;
    App.render();
}());