WebApp.Start System.NullReferenceException

Question

来自tutorial

System.NullReferenceException：'对象引用未设置为对象的实例。

示例不起作用：

<code>
        static void Main(string[] args)
        {
            // System.NullReferenceException: 'Object reference not set to an instance of an object.
            string url = "http://localhost:8080";
            using (WebApp.Start(url))
            {
                Console.WriteLine("Server running on {0}", url);
                Console.ReadLine();
            }
        }
</code>