code cleanup for phpstan level 4 (#1522)

src/EventSubscriber/TimezoneSubscriber.php

@@ -42,10 +42,6 @@ class TimezoneSubscriber implements EventSubscriberInterface
 
         $user = $this->storage->getToken()->getUser();
 
-        if (null === $user) {
-            return;
-        }
-
         if ($user instanceof User) {
             date_default_timezone_set($user->getTimezone());
         }

src/EventSubscriber/UserPreferenceSubscriber.php

@@ -67,7 +67,7 @@ class UserPreferenceSubscriber implements EventSubscriberInterface
         return $this->formConfig->getUserDefaultTheme();
     }
 
-    private function getDefaultCurrency(): ?string
+    private function getDefaultCurrency(): string
     {
         return $this->formConfig->getUserDefaultCurrency();
     }