Merge branch '4.4' into 5.2

* 4.4:
  [Finder] Fix gitignore regex build with "**"
  Fixed deprecation warnings about passing null as parameter
  [Security] Keep Bulgarian wording consistent across all texts.
  Migrate configuration file for PHP CS Fixer 2.19/3.0
  [Form] Replace broken ServerParams mock

Loader/XliffFileLoader.php

@@ -134,7 +134,7 @@ private function extractXliff1(\DOMDocument $dom, MessageCatalogue $catalogue, s
     private function extractXliff2(\DOMDocument $dom, MessageCatalogue $catalogue, string $domain)
     {
         $xml = simplexml_import_dom($dom);
-        $encoding = strtoupper($dom->encoding);
+        $encoding = $dom->encoding ? strtoupper($dom->encoding) : null;
 
         $xml->registerXPathNamespace('xliff', 'urn:oasis:names:tc:xliff:document:2.0');
 

Translator.php

@@ -446,7 +446,7 @@ protected function computeFallbackLocales(string $locale)
      */
     protected function assertValidLocale(string $locale)
     {
-        if (1 !== preg_match('/^[a-z0-9@_\\.\\-]*$/i', $locale)) {
+        if (null !== $locale && 1 !== preg_match('/^[a-z0-9@_\\.\\-]*$/i', $locale)) {
             throw new InvalidArgumentException(sprintf('Invalid "%s" locale.', $locale));
         }
     }