Kак решить вопрос,использую "SearchBar" и "JSON" в Xamarin,получить данную ошибку

Данная ошибка

 System.ArgumentNullException: 'Value cannot be null.
 Parameter name: source'

GetJSON

       private async void GetJSON()
        {

            //Check network status   
            if (NetworkCheck.IsInternet())
                {

                var client = new System.Net.Http.HttpClient();
                var response = await client.GetAsync("");
                string contactsJson = await response.Content.ReadAsStringAsync();

             //Converting JSON Array Objects into generic list  
            var ObjContactList = (Contact[])JsonConvert.DeserializeObject<Contact[]>(contactsJson);
            var descListOb = ObjContactList.OrderByDescending(x => x.Recovered);
            listviewConacts.ItemsSource = descListOb;


        }
            else
            {
                await DisplayAlert("JSONParsing", "No network is available.", "sex");
            }
            //Hide loader after server response    
            ProgressLoader.IsVisible = false;
        }

CountrySearchBar_TextChanged

        public List<Contact> Items { get; set; }
        private void CountrySearchBar_TextChanged(object sender, TextChangedEventArgs e)
     {
        var keyword = CountrySearchBar.Text;

        IEnumerable<Contact> sugggestions = Items.Where(c => 
        c.CombinedKey.ToLower().Contains(keyword.ToLower()));  

        listviewConacts.ItemsSource = sugggestions;
    }

JsonModel

public  class Contact
{
    [JsonProperty("provinceState")]
    public string ProvinceState { get; set; }

    [JsonProperty("countryRegion")]
    public string CountryRegion { get; set; }
 }


 }