Call to a member function path() on null

我有一个bug
如果我在blade.php文件里的<a href="{.......}">里写

        { $activity->subject->path() }

就会得到下图这个报错

Call to a member function path() on null (View: /Users/tg/Desktop/MyWork/forum/resources/views/profiles/activities/created_thread.blade.php) (View: /Users/tg/Desktop/MyWork/forum/resources/views/profiles/activities/created_thread.blade.php)

但是同样的，如果我用dd检测：

        { dd($activity->subject->path()) }

就会得到我应该有的路径

"/threads/python/68"

求问这是怎么回事？