Coerce empty $locale string to null to fix regression #135

Signed-off-by: George Steel <[email protected]>

src/Translator/Translator.php

@@ -345,6 +345,7 @@ public function getPluginManager()
      */
     public function translate($message, $textDomain = 'default', $locale = null)
     {
+        $locale      = $locale === '' ? null : $locale;
         $locale      = $locale ?? $this->getLocale();
         $translation = $this->getTranslatedMessage($message, $locale, $textDomain);