diff --git a/Traits/QueryTrait.php b/Traits/QueryTrait.php
index d6a9ee6..e35bf05 100644
--- a/Traits/QueryTrait.php
+++ b/Traits/QueryTrait.php
@@ -980,7 +980,7 @@ abstract class QueryTrait extends Component implements ActiveQueryInterface, ISq
      *
      * @return $this
      */
-    public function groupBy(string $name, string $having = NULL): static
+    public function groupBy(string $name, ?string $having = NULL): static
     {
         $this->group = $name;
         if (empty($having)) {