diff --git a/Chapter_17/Chapter_17.sql b/Chapter_17/Chapter_17.sql
index 4b2471d..ecb63c2 100644
--- a/Chapter_17/Chapter_17.sql
+++ b/Chapter_17/Chapter_17.sql
@@ -270,7 +270,7 @@ BEGIN
          OLD.grade,
          NEW.grade);
     END IF;
-    RETURN NEW;
+    RETURN NULL;
 END;
 $$ LANGUAGE plpgsql;