try
   {
    if (RetryPolicy == null) response = await httpClient.SendAsync(request, cancellationToken);
    else
    {
        // 失败重试
        await Retry.Invoke(async () =>
        {
            // 发送请求
            response = await httpClient.SendAsync(request, cancellationToken);
        }, RetryPolicy.Value.NumRetries, RetryPolicy.Value.RetryTimeout);
    }
}
catch (Exception ex)
{
    // 触发自定义事件
    if (response != null) OnRequestFailded(this, new HttpRequestFaildedEventArgs(request, response, ex));

    exception = ex;
}

System.NullReferenceException:“Object reference not set to an instance of an object.”