What version are you running?
4.0.x
What's the URL of the page containing the problem?
/r/<review id>/
What steps will reproduce the problem?

Open a review request to review
Click "Review" to open the review dialog
On the open review dialog, click "Publish Review"
Observe empty review published

Optional additional steps from 2. (not required, but these steps describe another use case where the user may add and delete comments and not realize they are posting an empty review):

3. Add Header text and general comment, click "Save" and "close" review dialog

4. Click "Review" to open the review dialog

5. Remove the header text and delete the general comment, click "Close"

6. Open the diff viewer and add a diff comment

7. Delete the diff comment (at this point, all comments added have been deleted)

8. In the draft review banner at the top of the screen, click "Publish Review"

9. Observe empty review published
What is the expected output? What do you see instead?
It is expected that the review will not be allowed to be published if there are no comments and no other content in the review.
Instead, we see that empty reviews can be published.
What operating system are you using? What browser?
macOS 10.13.6, Chrome Version 69