来自操作链接的控制器值始终为null

Question

有一个只需要一个字符串的视图

@model string

从ActionLink调用

@Html.ActionLink("Clinical Desktop", "Training", "Video"
    , new { play = "SomeVideo.mp4" }, null)

的视频控制器

public ActionResult Training(string play)
{
    return View(play);
}

play始终为空

手动调用URL

https://localhost:44300/Video/Training/play?SomeVideo.mp4