Calling Facebook photos using helpers METEOR-JS

Good morning everyone.

I'm trying to call facebook profile photos using the following in Meteor.

Template.foo.helpers({
    avatar: function() {
        if (Meteor.user().services.facebook) {
        return "http://ift.tt/rrPc6B" + Meteor    .user().services.facebook.id + "/picture/?type=large"; 
        }
        else
        {
            return "img/blank_avatar.png"
        }
    }
});

and I'm calling this by <img src = "{{avatar}}"> In my browser console, I'm getting an error saying Exception in template helper: avatar

I really don't understand what is the problem...