Render nothing caused by a comment

[a1mersnow]

Version

4.1.6

Reproduction link

https://github.com/a1mersnow/repro-comment

Steps to reproduce

1. visit /b
2. click 'to A'

What is expected?

rendering A

What is actually happening?

rendering nothing

---

However, if you remove the comment '' in Component TheB, the issue gone.

I meet the issue accidentally, it's very hard to discover/debug. At lease, we should warn in console, so the developer know how to fix it.

[LinusBorg]

this would rather be because of the transition than because of the router.

I'll move this issue to vue core.

[posva]

Duplicate of #4830