ReadAsStringAsync返回报错

  public class RequestHelper
    {
        private static readonly HttpClient _httpClient = new HttpClient();
        public static async Task<string> GetRequest(string url, string token = "")
        {
            var request = new HttpRequestMessage(HttpMethod.Get, url);
            request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); 
            if (!string.IsNullOrEmpty(token))
            {
                request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
            }
            
            var response = await _httpClient.SendAsync(request);
            response.EnsureSuccessStatusCode(); 
            //返回byte,转换成utf8,防止报错
            var bytes = await response.Content.ReadAsByteArrayAsync().ConfigureAwait(false);
            var str= Encoding.UTF8.GetString(bytes);
      
            return str;
            //return await response.Content.ReadAsStringAsync().ConfigureAwait(false);//直接返回json,有时候会报utf8不支持的错误
        }

    } 

使用ReadAsStringAsync调用api返回json时,有时会报如下错误

utf8' is not a supported encoding name. For information on defining a custom encoding, see the documentation for the Encoding.RegisterProvider method. (Parameter 'name')