MAGETWO-55858: Output escaping methods shouldn't be part of AbstractBlock

Author: Oleksandr Gorkun

lib/internal/Magento/Framework/View/Element/AbstractBlock.php

@@ -874,6 +874,10 @@ public function getModuleName()
      */
     public static function extractModuleName($className)
     {
+        if (!$className) {
+            return '';
+        }
+
         $namespace = substr(
             $className,
             0,