Fixed issue when there are no teachers

element/teachername/classes/element.php

@@ -48,8 +48,10 @@ class element extends \mod_customcert\element {
      * @return string the text
      */
     public function save_unique_data($data) {
+        if (!empty($data->teacher)) {
             return $data->teacher;
         }
+    }
 
     /**
      * Handles rendering the element on the pdf.