Fix styling

Author: tpetry

src/Helpers/ApiHelper.php

@@ -19,7 +19,7 @@ class ApiHelper
 
     public function __construct(
         private ?string $domain = 'https://explainmysql.com',
-        Client $client = null,
+        ?Client $client = null,
     ) {
         $this->client = $client ?? new Client();
     }

src/Values/QueryMetrics.php

@@ -55,8 +55,8 @@ public function __construct(
         string $version,
         array $explainTraditional,
         string $explainJson,
-        string $explainTree = null,
-        array $warnings = null,
+        ?string $explainTree = null,
+        ?array $warnings = null,
     ) {
         $this->query = $query;
         $this->version = $version;