E_WARNING: strpos(): Empty needle

@domainsupport Can you please let me know the PHP version your site is running on and the WooCommerce version currently active on your site?

PHP v7.4.30, WooCommerce v8.0.2

This is happening because on line 141 of /product-input-fields-for-woocommerce/includes/alg-wc-pif-functions.php …

$jqueryui_format .= ( isset( $symbols_matching[ $char ] ) && strpos( $jqueryui_format, $symbols_matching[ $char ] ) !== false ) ? $symbols_matching[ $char ] : $char;

… you are using isset( $symbols_matching[ $char ] ) to check if an array element exists but this is not sufficient because some of the array elements are empty strings. So you need to use this instead isset( $symbols_matching[ $char ] ) && $symbols_matching[ $char ]

The line should then read as follows …

$jqueryui_format .= ( isset( $symbols_matching[ $char ] ) && $symbols_matching[ $char ] && strpos( $jqueryui_format, $symbols_matching[ $char ] ) !== false ) ? $symbols_matching[ $char ] : $char;

… and the warning will not be shown.

Oliver