List files and folders in dropbox sdk

I need to get the list of files and folders from my account with dropbox SDK .Net. Simple Code :

static async Task ListRootFolder(DropboxClient dbx)
    {
        var list = await dbx.Files.ListFolderAsync(string.Empty);
        foreach (var item in list.Entries.Where(i => i.IsFolder))
        {
            Console.WriteLine("D  {0}/", item.Name);
        }

        foreach (var item in list.Entries.Where(i => i.IsFile))
        {
            Console.WriteLine("F{0,8} {1}", item.AsFile.Size, item.Name);
        }
    }

dbx object - is correct, but list is null. no one files in Console, but they are exists in account.

Message = "Cannot access a disposed object.\r\nObject name: 'System.Net.Http.HttpClient'."

Where is a error ?