Fix PHP 8.5 deprecated errors

Author: kukulich

src/Scanner/Scanner.php

@@ -19,6 +19,11 @@ public function __construct(Translations ...$allTranslations)
     {
         foreach ($allTranslations as $translations) {
             $domain = $translations->getDomain();
+
+            if (is_null($domain)) {
+                $domain = '';
+            }
+
             $this->translations[$domain] = $translations;
         }
     }
@@ -57,6 +62,10 @@ protected function saveTranslation(
             $domain = $this->defaultDomain;
         }
 
+        if (is_null($domain)) {
+            $domain = '';
+        }
+
         if (!isset($this->translations[$domain])) {
             return null;
         }