Google search critical

Hi, I recently updated the plugin, one day later Google reports a critical issue on my website:

Search Console has identified that your site is affected by 2 Review snippets structured data issue(s). The following issues were found on your site.
Top critical issues*:
Either “ratingCount” or “reviewCount” should be specified
Missing field “ratingValue”
*Critical issues prevent your page or feature from appearing in Search results.
We recommend that you fix these issues when possible to enable the best experience and coverage in Google Search.

The problem is that it can find properties it want to use, but they hold no values.

“ratingValue”: “”,
“reviewCount”: “”

piece of html where it appears

{
“@context”: “https://schema.org”,
“@type”: “Book”,
“name”: “Flip, Grote Vriend en corona”,
“author”: {
“@type”: “Person”,
“name”: “Mattanja Nieuwburg”
},
“image”: “https://www.bookabooka.com/wp-content/uploads/2020/09/0_front_cover-25-e1601321137121.jpg”,
“aggregateRating”: {
“@type”: “AggregateRating”,
“ratingValue”: “”,
“reviewCount”: “”
}
}

I can see a “display rating” checkbox under “gallery settings” but it is unchecked.
My website does not support rating books.
How can I remove these values from the html?

The page I need help with: [log in to see the link]