.NETCORE MVC SelectList 绑定报错 System.NullReferenceException:“Object reference not set to an instance of an object.”

解决方法：

原来绑定键值对的时候，用了小写的key和value，换成大写的

SelectList mList = new SelectList(mli, "Key", "Value", 1);
ViewData["ddlMenu"] = mList;