What can return else the “content” attribute of template element

I asked this question in whatwg repo, but issue was closed almost instantly with reason like: “this sort of question for SO”. Let’s test SO for knowing of whatwg spec 🙂

Whatwg spec says the next:

The content getter steps are to return template’s template contents,
if the template contents is not a ShadowRoot node; otherwise null.

Could you show me example when template.content returns null?