Nested array giving error

[celsomtrindade]

When I use a nested array, I keep getting an error on this line here:

var array = collection.filter(function(item){
    return !item.container;
}).map(function(item){
    return {
        part: item.getPart().id,
        y: item.element[0].getBoundingClientRect().top //Here is where the console point to
    };
});

My array looks like this:

[
    {
        "id":"1",
        "name": "Shoes",
        "items": [
            {"id":"1", ...},
            {"id":"2", ...},
            {"id":"3", ...},
        ]
    },
    {
        "id":"2",
        "name": "Dress",
        "items": [
            {"id":"4", ...},
            {"id":"5", ...},
            {"id":"6", ...},
        ]
    },
    {
        "id":"3",
        "name": "Tie",
        "items": [
            {"id":"7", ...},
            {"id":"8", ...},
            {"id":"9", ...},
        ]
    }
]

But the only one I want to filter is the main array, not the items. Everything works fine as expected. But there is this error appearing everytime I move an item. Like I said, this error is not stoping the sorting,drag, drop functionality, but still there is this error.

My HTML:

<section sv-root sv-part="vm.category" sv-on-sort="vm.sortList()">
    <div ng-repeat="item in vm.category track by item.id" sv-element>
        <div><h4>{{category.name}}</h4></div>

        <div class="row">
            <div class="col" ng-repeat="product in category.items"></div>
        </div>
    </div>
</section>