diff --git a/src/helper.php b/src/helper.php
index f2f47f3..e61d13f 100644
--- a/src/helper.php
+++ b/src/helper.php
@@ -8,7 +8,7 @@
  * @param array|null $arr Original Array
  * @return Raggitech\DotArray\DotArray
  */
-function dot(array $arr = NULL)
+function dot(?array $arr = NULL)
 {
     return new DotArray($arr);
 }