Xamarin Erro CS0161 GetResponse <t>（字符串，字符串，字符串）'：并非所有代码路径都返回一个值

Question

我有这个代码，但是我收到了一个错误：错误CS0161'ApiCall.GetResponse（string，string，string）'：并非所有代码路径都返回值

public class ApiCall
{
    static readonly string ApiUrl = "http://localhost:1762/api/{0}/{1}?{2}";

    public async Task<T> GetResponse<T>(string controller, string method, string prm) where T : class
    {

        var client = new System.Net.Http.HttpClient();


        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));


        var response = await client.GetAsync(string.Format(ApiUrl, controller, method, prm));
        var JsonResult = response.Content.ReadAsStringAsync().Result;

        if (typeof(T) == typeof(string))
            return null;

        var rootobject = JsonConvert.DeserializeObject<T>(JsonResult);
            return rootobject;
   }
 }
}

有人知道吗？