diff --git a/tests/TestSuite7.php b/tests/TestSuite7.php
index fd1977a8ca..1b651519dd 100644
--- a/tests/TestSuite7.php
+++ b/tests/TestSuite7.php
@@ -23,7 +23,7 @@ class TestSuite extends PHPUnit_TestSuite
      *
      * @return \PHPUnit\Framework\TestResult
      */
-    public function run(TestResult $result=null): TestResult
+    public function run(?TestResult $result=null): TestResult
     {
         $result = parent::run($result);
         printPHPCodeSnifferTestOutput();