data-* attributes in select2?

Question

JavaScript

There is a code:

$('.itemName').select2({
    placeholder: 'Введите перенесенные болезни, можно вводить название или код МКБ',
        ajax: {
            url: "{{route('getRequestmkb10')}}",
            dataType: 'json',
            delay: 250,
            processResults: function (data) {
                return {
                    results: $.map(data, function (item) {
                        return {
                            text: item.value+' :: '+item.text,
                            id: item.id,
                            title: item.value,
                            disease: item.text
                        }
                        // alert(item.id);
                    })
                };
            },
            cache: true
        }
    });

And the select itself:

<select id="cn_ds" class="itemName form-control" style="width:100%;" name="f_sickness[]" value="{{old('f_sickness')}}" multiple data-ajax--disease=""></select>

I want to add an arbitrary data-disease attribute. But no matter how I tried, nothing worked. Off. quite a few examples are devoted to this issue in the documentation.