AC-2003: Fix subset of deprecated php usages

- Fix deprecated use of null

Author: Rrego6

lib/internal/Magento/Framework/View/Page/Config.php

@@ -193,10 +193,11 @@ public function __construct(
         $this->title = $title;
         $this->localeResolver = $localeResolver;
         $this->isIncludesAvailable = $isIncludesAvailable;
+        $locale = $this->localeResolver->getLocale();
         $this->setElementAttribute(
             self::ELEMENT_TYPE_HTML,
             self::HTML_ATTRIBUTE_LANG,
-            strstr($this->localeResolver->getLocale(), '_', true)
+            $locale !== null ? strstr($locale, '_', true) : ''
         );
         $this->escaper = $escaper ?? ObjectManager::getInstance()->get(
             Escaper::class