Invalid magic findWhere ()

I am building an application with Backbone and RequireJS and I am incredibly confused by the behavior of the Collection.findWhere()Backbone function here .

When the code is this:

var myId = 1;
var subList = parentList.findWhere({id: myId});

subList is displayed as undefined.

When the code is this:

var subList = parentList.findWhere({id: 1});

subList contains the correct model.

Does anyone know what can do this?