Minor - Remove notice

main/document/edit_document.php

@@ -591,7 +591,8 @@ function show_return($document_id, $path, $call_from_tool='', $slide_id=0, $is_c
     $url = api_get_path(WEB_CODE_PATH).'document/document.php?'.api_get_cidreq().'&id='.$parent_id;
 
 	if ($is_certificate_mode) {
-		echo '<a href="document.php?curdirpath='.Security::remove_XSS($_GET['curdirpath']).'&selectcat=' . Security::remove_XSS($_GET['selectcat']).'">'.
+		$selectedCategory = (isset($_GET['curdirpath']) ? Security::remove_XSS($_GET['curdirpath']) : '');
+		echo '<a href="document.php?curdirpath='. $selectedCategory .'&selectcat=' . $selectedCategory .'">'.
             Display::return_icon('back.png',get_lang('Back').' '.get_lang('To').' '.get_lang('CertificateOverview'),'',ICON_SIZE_MEDIUM).'</a>';
 	} elseif($call_from_tool=='slideshow') {
 		echo '<a href="'.api_get_path(WEB_PATH).'main/document/slideshow.php?slide_id='.$slide_id.'&curdirpath='.Security::remove_XSS(urlencode($_GET['curdirpath'])).'">'.