Select2 passing null parameters to controller

How Do I...
#1

Hello - my boss wants me to implement select2 for a new feature. I’m having a weird issue where it’s passing null params to the controller for filtering. I’ve tried your syntax and the other solutions on stackoverflow, but no dice. Here’s the JS, i included both ajax calls I’ve tried. We also tried hard-coding the params:

$(".filter-advertisers").select2({
            //data: filterSelect,
            ajax: {
                url: 'Home/GetFilterAdvertiser',
                data: function (params) {
                    var query = {
                        search: params.term,
                    }
                    return query
                },
                processResults: function (data) {
                    //advertisers = $.map(data, function (obj) {
                    //    obj = { id: i, text: obj }

                    //    i = i + 1;
                    //    return obj
                    //})
                    return {
                        results: data
                    }
                }
            },
            placeholder: 'Advertisers',
            closeOnSelect: false,
            minimumInputLength: 4,
            allowClear: true,
            width: '150',
            multiple: true
        });


$(".filter-agencies").select2({
            ajax: {
                cache: false,
                datatype: 'JSON',
                type: 'GET',
                url: 'Home/GetFilterAgency',
                data: function (params) {
                    return {q:params}
                    //var query = {
                    //    search: params.term
                    //}
                    //return query
                },
                processResults: function (data) {
                    return {
                        results: data
                    }
                }
            },
            placeholder: 'Agencies',
            width: '150',
            multiple: true,
            closeOnSelect: false,
            minimumInputLength: 4
            //tags: true
        });

C#:

[HttpGet]
        public string GetFilterAdvertiser(string query)
        {
            var x = _orderedLinesProcessor.GetFilterAdvertiser();
            var i = 0;
            var dict = new Dictionary<int, string>();
            foreach (var el in x)
            {
                dict.Add(i, el);
                i += 1;
            }

            return JsonConvert.SerializeObject(dict);
        }

Thanks for your time.

#2

the solution was to change the method argument to:

public string GetFilterAdvertiser(string search){}