Fix php warning

main/gradebook/lib/be/surveylink.class.php

@@ -276,13 +276,17 @@ class SurveyLink extends AbstractLink
         return null;
     }
 
+    /**
+     * @return array|bool|mixed
+     */
     private function get_survey_data()
     {
         $tbl_name = $this->get_survey_table();
         $session_id = api_get_session_id();
+
         if ($tbl_name == '') {
             return false;
-        } elseif (!isset($this->survey_data)) {
+        } elseif (empty($this->survey_data)) {
             $sql = 'SELECT * FROM '.$tbl_name.'
                     WHERE
                         c_id = '.$this->course_id.' AND
@@ -302,6 +306,5 @@ class SurveyLink extends AbstractLink
     private static function html_to_text($string)
     {
         return strip_tags($string);
-        //return trim(api_html_entity_decode(strip_tags(str_ireplace(array('<p>', '</p>', '<br />', '<br/>', '<br>'), array('', ' ', ' ', ' ', ' '), $string)), ENT_QUOTES));
     }
 }