This suggestion is to make the "path" parameter optional for the function http://example.com/rest/api/1.0/projects/{projectKey}/repos/{repositorySlug}/pull-requests/{pullRequestId}/comments, since general comments on pull requests aren't anchored to a path, thus you can't get them using this function - currently it's only possible to get comments from files using it.

If you try not setting the "path", the return is:

{"errors":[{"context":null,"message":"The path query parameter is required when retrieving comments.","exceptionName":null}]}