check classes may not have action links, they are allowed to return null.

However here the code assumes it always has an action link:

https://github.com/moodle/moodle/blob/ecfcf00d92df2e874da9d8cb31750403ada7789a/lib/adminlib.php#L11813

But if a check doesn't, it throws an exception:

Exception - renderer_base::render(): Argument #1 ($widget) must be of type renderable, null given, called in [dirroot]/lib/adminlib.php on line 11813