面对 PHP 8 警告：尝试读取 null 上的属性“query”

问：

在运行 PHP 8 时，收到这部分代码的 PHP 警告：

function wpsc_body_class( $classes ) {
global $wp_query, $wpsc_query;

$post_id = get_the_ID();

if ( $post_id ) {

    $page_url = get_permalink( $post_id );

    // If on a product or category page...
    if ( get_option( 'product_list_url' ) == $page_url || get_post_type( $post_id ) === 'wpsc-product' ) {

        $classes[] = 'wp-e-commerce';

        if ( ! is_array( $wpsc_query->query ) ) {
            $classes[] = 'wpsc-home';
        }

        if ( wpsc_is_single_product() ) {
            $object    = $wp_query->get_queried_object();
            $classes[] = 'wpsc-single-product';
            if ( absint( $object->ID ) > 0 ) {
                $classes[] = 'wpsc-single-product-' . absint( $object->ID );
            }
        }

        if ( wpsc_is_in_category() && ! wpsc_is_single_product() ) {
            $classes[]  = 'wpsc-category';
            $tax_object = $wp_query->get_queried_object();
            $classes[]  = 'wpsc-category-' . esc_attr( $tax_object->slug );
        }

        if ( wpsc_is_in_tag() && ! wpsc_is_single_product() ) {
            $classes[]  = 'wpsc-tag';
            $tax_object = $wp_query->get_queried_object();
            $classes[]  = 'wpsc-tag-' . esc_attr( $tax_object->slug );
        }
    }

    $page_url = set_url_scheme( $page_url, 'relative' );

    // If viewing the shopping cart...
    if ( set_url_scheme( get_option( 'shopping_cart_url' ), 'relative' ) === $page_url ) {
        $classes[] = 'wp-e-commerce';
        $classes[] = 'wpsc-shopping-cart';
    }

    // If viewing the transaction...
    if ( set_url_scheme( get_option( 'transact_url' ), 'relative' ) === $page_url ) {
        $classes[] = 'wp-e-commerce';
        $classes[] = 'wpsc-transaction-details';
    }

    // If viewing your account...
    if ( set_url_scheme( get_option( 'user_account_url' ), 'relative' ) === $page_url ) {
        $classes[] = 'wp-e-commerce';
        $classes[] = 'wpsc-user-account';
    }
}

return $classes;

}

指向此代码行时出错：

if ( ! is_array( $wpsc_query->query ) ) {

寻找解决此问题的最佳方法，并更改此代码，以克服尝试读取 null 上的属性“query”的 php 8 警告。