无法识别ExceptionFilterAttribute中的自定义异常类型

Question

我正在使用.NET Core 3.1。我使用ExceptionFilterAttribute处理整个应用程序中的错误。我还具有一个称为WarningException的自定义异常类。问题是WarningException类型在ExceptionFilterAttribute中未被识别为WarningException，但被识别为System.Exception。怎么可能呢？

public class CustomErrorAttribute : ExceptionFilterAttribute
{
    public override void OnException(ExceptionContext context)
    {
        base.OnException(context);

        if (context.ExceptionHandled)
            return;

        context.ExceptionHandled = true;

        int statusCode = 500;
        string status = "Internal Server Error";
        string header = "Internal Server Error";

        if (context.Exception is WarningException) //exception does not pass this `if`
        {
            var ex = context.Exception as WarningException;
            statusCode = (int)ex.StatusCode;
            status = ex.Status;
            header = "Warning";
        }
    }
}

public class WarningException : Exception
{
    public WarningException(string message)
        : base(message)
    {
    }
    public HttpStatusCode StatusCode => HttpStatusCode.NoContent;
    public string Status => "No Content";
}

public ActionResult Index()
{
    throw new WarningException("This custom error should be catched as WarningException NOT System.Exception");
}