GetSingleCategoryRecords() is doesn't working in WinForms

[FlashJ1]

Hi, mirrorcult! In my project (WinForms .net framework 4.8 is required in NuGet) I can't init Leaderboard, but in console is working no problem. He's throwing except about GenericArguments[0], Nullable TClass

using SpeedrunDotComAPI;
using SpeedrunDotComAPI.Categories;
using SpeedrunDotComAPI.Games;
using SpeedrunDotComAPI.Leaderboards;
using SpeedrunDotComAPI.Runs;
using SpeedrunDotComAPI.Links;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Text.Json;

namespace SpeedrunDotCom_APP2
{
    public partial class Form1 : Form
    {
        public SRCApiClient src;

        public CategoryModel[] categories;
        public Form1()
        {
            InitializeComponent();

            src = new SRCApiClient();

        }

        private async void btFind_Click(object sender, EventArgs e)
        {
            

            cbCategories.Items.Clear();

            string gameName = tbSearchGame.Text;

            //GameModel[] filteredGame = await src.Games.GetAllGames(new GameFilterOptions() { Name = gameName, _Bulk = true });

            CategoryModel[] categories = await src.Games.GetSingleGameCategories(gameName);

            if (categories == null)
            {
                MessageBox.Show("Failed ID");
            }
            else
            {
                MessageBox.Show("Success ID");
            }

                cbCategories.DisplayMember = "Name";

            foreach (var category in categories)
            {
                cbCategories.Items.Add(category);
            }
        }
        private async void cbCategories_SelectedIndexChanged(object sender, EventArgs e)
        {
            try
            {

                //string gameName = tbSearchGame.Text;

                //CategoryModel currCategory = (CategoryModel)cbCategories.SelectedItem;

                //LeaderboardModel[] leaderboard = await src.Categories.GetSingleCategoryRecords(currCategory.Id);

                //Task t1 = Task.Run(() => { LeaderboardInitAsync(); });

                //LeaderboardModel[] leaderboard = await LeaderboardInitAsync();



                // this example is doesn't working neither

                CategoryModel[] sm64Categories = await src.Games.GetSingleGameCategories("sm64");
                CategoryModel seventyStar = sm64Categories.First(c => c.Name == "70 Star");
                LeaderboardModel[] leaderboards = await src.Categories.GetSingleCategoryRecords(seventyStar.Id); // Returns a list of leaderboards because of categories with ILs.
                RunPlaceModel worldRecord = leaderboards[0].Runs.First(r => r.Place == 1);


                //RunPlaceModel worldRecord = leaderboard[0].Runs.First(r => r.Place == 1);

                lbUsername.Text = worldRecord.Run.Comment;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.StackTrace);
                MessageBox.Show(ex.Message);
            }
            
        }
    }
}