I get an error in WordPress function when I filter the page's alias

Question

This works fine on the store page but throws an error on other pages.

This has to do with if(is_page('shop')).

function divi_engine_body_class( $classes ) {
   if(is_page('shop')) {
        $classes[] = 'woocommerce-page-SGARAGLINO';
        return $classes;
    }
}
add_filter('body_class','divi_engine_body_class',99999);

Error message: PHP Fatal Error: Uncaught TypeError: array_unique(): Parameter #1 ($array) must be of type array, in /wordpress/core/6.2.2/wp-includes/post-template.php: Null is given at 861.

Answer 1

This function only returns the $classes variable if is_shop() is true, when in fact it should always return the $classes variable:

function divi_engine_body_class( $classes ) {
   if ( is_page( 'shop' ) ) {
        $classes[] = 'woocommerce-page-SGARAGLINO';
    }

    return $classes;
}

Filters must always return a value; if they do not return a value, an error will almost always be raised.