if possible, it would be probably the easiest if you can ensure that all reviews that you add to CPT, have content. Or at least if there is no content, that it’s not published.
WP_Query does not have a direct parameter for checking content emptiness, that’s the issue here. And if you need that, you will have to use a filter like Filter: bricks/query/result – Bricks Academy
An alternative to the above would be to use a custom field for the content of the reviews, and set the condition for that field, rather than the default content field