MMinor - Avoid notice

main/admin/settings.php

@@ -83,7 +83,7 @@ $form_search = new FormValidator('search_settings', 'get', api_get_self() , null
 $form_search->addElement('text', 'search_field');
 $form_search->addElement('hidden', 'category', 'search_setting');
 $form_search->addElement('style_submit_button', 'submit_button', get_lang('Search'), 'value="submit_button", class="search"');         
-$form_search->setDefaults(array('search_field' => $_REQUEST['search_field']));
+$form_search->setDefaults(array('search_field' => (isset($_REQUEST['search_field'])?$_REQUEST['search_field']:null)));
 
 $form_search_html = $form_search->return_form();
 
@@ -505,4 +505,4 @@ if (!empty($_GET['category'])) {
 }
 
 /* FOOTER */
-Display :: display_footer();
+Display :: display_footer();