diff --git a/Classes/Service/ImpersonateService.php b/Classes/Service/ImpersonateService.php
index e148508..9d1c845 100644
--- a/Classes/Service/ImpersonateService.php
+++ b/Classes/Service/ImpersonateService.php
@@ -169,7 +169,7 @@ protected function writeSession(string $key, ?string $value): void
      * @param string $key
      * @throws SessionNotStartedException
      */
-    protected function getSessionData(string $key): ?mixed
+    protected function getSessionData(string $key)
     {
         return $this->session->isStarted() && $this->session->hasKey($key) ? $this->session->getData($key) : null;
     }