private async void SearchForDocumentAdvanced(string query, string filter, string facet_field, string facet_query)
        {
            IsBusy = true;
            SolrDocService service = new SolrDocService();

            ListOfDocuments = await service.SendQueryRequestAdvanced_Rest(query, filter, facet_field, facet_query);

            IsBusy = false;
        }
        private async void SearchForDocument(string term)
        {
            IsBusy = true;
            SolrDocService service = new SolrDocService();

            ListOfDocuments = await service.SendQueryRequest_Rest(term, new SolrQuery());

            IsBusy = false;
        }