使用 XML 调用 Web API 时出现 500 错误

我在.net 4.5中开发了一个Web API。 当我测试 api 调用时，我收到 500 错误。 此行为仅在我发送 XML 时发生。 如果我使用表单URL编码字符串的JSON，服务器可以正确处理请求。

我添加了

GlobalConfiguration.Configuration.IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Always;

到 WebApiConfig .cs返回的错误是：

<Error><Message>An error has occurred.</Message><ExceptionMessage>Object reference not set to an instance of an object.</ExceptionMessage><ExceptionType>System.NullReferenceException</ExceptionType><StackTrace>   at System.Web.Http.ApiController.&lt;InvokeActionWithExceptionFilters&gt;d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
  at System.Web.Http.Dispatcher.HttpControllerDispatcher.&lt;SendAsync&gt;d__0.MoveNext()</StackTrace></Error>

我的标题是：

User-Agent: Fiddler
Content-Type: application/xml; charset=utf-8
Host: corebeta.pexcard.com
Content-Length: 119

我的要求是：

<Admin.CardListRequest>
<username>TestUser</username>
<password>GoodPassword</password>
</Admin.CardListRequest>

我的类看起来像这样：

public class CardListRequest{
    public string UserName { get; set; }
    public string Password { get; set; }
}

WebAPI 代码如下所示（log 正在使用 log4net，并且没有写入该日志）：

    /// <summary>
    /// Gets the list of open cardholders
    /// </summary>
    /// <param name="UserName">The username you use to log on to pexcardadmin.com</param>
    /// <param name="Password">The password you use to log on to pexcardadmin.com</param>
    /// <returns>A list of cardholders with balances</returns>
    [HttpGet]
    public List<Admin.Account> CardList(string UserName, string Password)
    {
        try
        {
            log.Info(String.Format("Admin Parameters: <UserName={0}>", UserName));
            AuthenticateApi(UserName, Password, "cardList");
            var Ret = GetCoreCardCardList(UserName, Password);
            APIData.Response = "Success";

            return Ret;
        }
        catch (Exception e)
        {
            log.Error(e);
            APIData.Response = e.Message;
            throw e;
        }
        finally
        {
            APIData.ResponseTime = DateTime.Now;
            APILog.LogAPI(APIData);
        }
    }
    /// <summary>
    /// Gets the list of open cardholders
    /// </summary>
    /// <param name="Req"> The Request Parameter</param>
    /// <returns>A list of cardholders with balances</returns>
    [HttpPost]
    public List<Admin.Account> CardList(Admin.CardListRequest Req)
    {
        APIData.ParamBlob = JsonConvert.SerializeObject(Req);
        return CardList(Req.UserName, Req.Password);
    }

有没有人对为什么抛出此错误有任何想法？

谢谢史蒂文