Sending email to multiple customers cause this error:

Fatal error: Cannot use object of type queryFactoryResult as array in admin/includes/modules/newsletters/product_notification.php on line 219

solution:

in admin/includes/modules/newsletters/product_notification.php on line 219

change:

'email_address' => $customers->['customers_email_address']);

to

'email_address' => $customers->fields['customers_email_address']);