protected function tryNsInstance($class, $subNamespace, $namespace)
    {
        $fqClass = $this->getFqClass($class, $subNamespace, $namespace);
        $fileName = $this->getFileName($fqClass);
        // Checking if the file exists prevents warnings in Magento whose own
        // autoloader logs warnings when a class cannot be loaded.
        return is_readable($fileName) && class_exists($fqClass) ? $fqClass : '';
    }