return null explicitly for nullable return types

app/Services/IndieAuthService.php

@@ -26,7 +26,7 @@ class IndieAuthService
     {
         $endpoint = $this->client->discoverAuthorizationEndpoint($this->client->normalizeMeURL($domain));
         if ($endpoint === false) {
-            return;
+            return null;
         }
 
         return $endpoint;

app/Services/TokenService.php

@@ -45,7 +45,7 @@ class TokenService
         try {
             $token = (new Parser())->parse((string) $token);
         } catch (InvalidArgumentException | RuntimeException $e) {
-            return;
+            return null;
         }
         if ($token->verify($signer, config('app.key'))) {
             //signuture valid