diff --git a/src/db/quiz/QuizDAO.ts b/src/db/quiz/QuizDAO.ts
index 9b396eea47667c4cd469ada93771322640e8769d..3d91283b106ba9b1a833112c3f54a16e9012f543 100644
--- a/src/db/quiz/QuizDAO.ts
+++ b/src/db/quiz/QuizDAO.ts
@@ -261,7 +261,7 @@ class QuizDAO extends AbstractDAO<Array<IQuizEntity>> {
   }
 
   private replaceTypeInformationOnLegacyQuiz(obj): object {
-    if (typeof obj !== 'object') {
+    if (obj === null || typeof obj !== 'object') {
       return obj;
     }