Fix #7893

Fix bug where ClassGenerator generates class with empty namespace fixes

Author: andreaspenz

lib/internal/Magento/Framework/Code/Generator/ClassGenerator.php

@@ -206,10 +206,10 @@ protected function createMethodGenerator()
     }
 
     /**
-     * {@inheritdoc}
+     * @return string|null
      */
     public function getNamespaceName()
     {
-        return ltrim(parent::getNamespaceName(), '\\');
+        return ltrim(parent::getNamespaceName(), '\\') ?: null;
     }
 }