_wp_upgrade_revisions_of_post example

$revisions = wp_get_post_revisions(
            $post_id,
            array(
                'order'          => 'ASC',
                'posts_per_page' => 1,
            )
        );
        $revision  = current( $revisions );

        // Check if the revisions have been upgraded.         if ( $revisions && _wp_get_post_revision_version( $revision ) < 1 ) {
            _wp_upgrade_revisions_of_post( $post, wp_get_post_revisions( $post_id ) );
        }
    }

    if ( isset( $post_data['visibility'] ) ) {
        switch ( $post_data['visibility'] ) {
            case 'public':
                $post_data['post_password'] = '';
                break;
            case 'password':
                unset( $post_data['sticky'] );
                break;