diff --git a/src/Issue/IssueSearchResult.php b/src/Issue/IssueSearchResult.php
index 27b3e9b..9ba8bd4 100644
--- a/src/Issue/IssueSearchResult.php
+++ b/src/Issue/IssueSearchResult.php
@@ -17,7 +17,7 @@ class IssueSearchResult
     /**
      * @var string
      */
-    public $expand;
+    public ?string $expand = null;
 
     /**
      * @var int
@@ -114,17 +114,14 @@ public function getIssue($ndx)
     }
 
     /**
-     * @return string
+     * @return ?string
      */
     public function getExpand()
     {
         return $this->expand;
     }
 
-    /**
-     * @param string $expand
-     */
-    public function setExpand($expand)
+    public function setExpand(?string $expand)
     {
         $this->expand = $expand;
     }