如果等待url.GetStringAsync null，C#如何重试？

using System;
using System.Net.Http;
using System.Threading.Tasks;

public class Program
{
    public static async Task Main()
    {
        string url = "http://example.com";
        int maxRetryCount = 3; // 最大重试次数

        string result = await GetStringWithRetry(url, maxRetryCount);
        Console.WriteLine(result);
    }

    private static async Task<string> GetStringWithRetry(string url, int maxRetryCount)
    {
        int retryCount = 0;
        string result = null;

        while (retryCount < maxRetryCount && result == null)
        {
            try
            {
                using (var client = new HttpClient())
                {
                    result = await client.GetStringAsync(url);
                }
            }
            catch (Exception)
            {
                // 发生异常，重试
                retryCount++;
            }
        }

        return result;
    }
}