Checking that some variables exist before using it.

renderer.php

@@ -408,7 +408,7 @@ class format_iena_renderer extends format_topics_renderer{
 			}
 
 			$titre = $nameSection[$i];
-			$sectionIntro = $introSection[$i];
+			$sectionIntro = isset($introSection[$i]) ? $introSection[$i] : '';
 						//If section is hidden continue
 			if ($titre == null && !(has_capability('moodle/course:update', $context = context_course::instance($COURSE->id), $USER->id))) {
 				$i++;