diff --git a/tests/Console/Output/GitlabOutputFormatterTest.php b/tests/Console/Output/GitlabOutputFormatterTest.php
index c9288a6df6..8d5cb4b471 100644
--- a/tests/Console/Output/GitlabOutputFormatterTest.php
+++ b/tests/Console/Output/GitlabOutputFormatterTest.php
@@ -154,7 +154,7 @@ private function path(string $path): string
     /**
      * @return array{CodingStandardError[], FileDiff[]}
      */
-    private function getMockedIssues(string $filePathForChanges = null): array
+    private function getMockedIssues(?string $filePathForChanges = null): array
     {
         $filePathForOriginal = $this->path('/Source/RandomFile.php');