Merge pull request #21168 from Yoast/1394-major-222-image-object-shou…

…ld-not-be-output-on-webpage-and-article-in-case-image-was-not-added-to-the-post

Make sure image is null when it is '' so that the schema generator does not create an empty record.

src/context/meta-tags-context.php

@@ -758,7 +758,11 @@ private function get_main_image_url_for_rest_request() {
 		switch ( $this->page_type ) {
 			case 'Post_Type':
 				if ( $this->post instanceof WP_Post ) {
-					return $this->image->get_post_content_image( $this->post->ID );
+					$url = $this->image->get_post_content_image( $this->post->ID );
+					if ( $url === '' ) {
+						return null;
+					}
+					return $url;
 				}
 				return null;
 			default: