title: Prestashop - Strict Standards if I install a module
body: <p>In Prestashop 1.6.1.13, when I create an order from the admin panel, and I search for products to add to it, I have this php error and I can't search any product:</p>
  
  <pre><code>Strict Standards: Declaration of Product::_getCustomizationFieldsNLabels() 
  should be compatible with ProductCore::_getCustomizationFieldsNLabels($product_id, $id_shop = NULL) 
  in /web/htdocs/www.lab-biocompany.com/home/eshop/override/classes/Product.php on line 810
  
  Strict Standards: Declaration of Product::_createLabel() 
  should be compatible with ProductCore::_createLabel($languages, $type) 
  in /web/htdocs/www.lab-biocompany.com/home/eshop/override/classes/Product.php on line 810
  
  Strict Standards: Declaration of Product::getCustomizationFields() 
  should be compatible with ProductCore::getCustomizationFields($id_lang = false, $id_shop = NULL) 
  in /web/htdocs/www.lab-biocompany.com/home/eshop/override/classes/Product.php on line 810
  </code></pre>
  
  <p>I have this issue if I install a module 'A'. If I uninstall the module 'A', I haven't the issue. But this module doesn't override the class Product, that instead is overrided by another module. How is it possible?</p>
  
  <p>However the module 'A' has two overrides of two controllers instead. But they are unrelated to the Product class.</p>
  
  <p><strong>Update 1</strong></p>
  
  <p>I solved this problem setting 'Disable all overrides' to 'No' in the Prestashop Settings.</p>
  
  <p>Now I can search products but I can't add them to the order. I get this error:</p>
  
  <pre><code>Warning: Cannot modify header information - headers already sent by (output started 
  at /var/www/html/prestashop-1.6/prestashop/controllers/admin/AdminCartsController.php:481) 
  in /var/www/html/prestashop-1.6/prestashop/classes/controller/AdminController.php on line 1829
  </code></pre>
  
  <p>and it happens when my custom module 'A' is installed. If I delete del folder 'override' from the module and I install it, I get the same error.</p>
  
  <p><strong>Update 2</strong></p>
  
  <p>Solved. My error was that in the principal file of my module I write this code (in order to see php errors) before the beginning of the class:</p>
  
  <pre><code>ini_set('display_errors', 1);
  ini_set('display_startup_errors', 1);
  error_reporting(E_ALL);
  
  class MyModule extends Module {
  ...
  }
  </code></pre>
  
  <p>Deleting these three lines, all works fine.</p>