add premium post class in module

function jnews_post_class( $class = '', $post_id = null ) {
    $post_type = get_post_type( $post_id );
    // Post Format.
    if ( $post_type && post_type_supports( $post_type, 'post-formats' ) ) {
        $post_format = get_post_format( $post_id );

        if ( $post_format && ! is_wp_error( $post_format ) ) {
            $class .= ' format-' . sanitize_html_class( $post_format );
        } else {
            $class .= ' format-standard';
        }
    }

    if ( jeg_metabox( 'jnews_paywall_metabox.enable_premium_post', false, $post_id ) ) {
        $class .= ' premium-post';
    }

    return 'class="' . $class . '"';
}