public function getFullyQualifiedClassName(string $className, string $defaultNamespace) : string
    {
        $rootNamespace = $this->getRootNamespace();

        // If the class name is already fully-qualified
        if (mb_strpos($className, $rootNamespace) === 0) {
            return $className;
        }

        return trim($defaultNamespace, '\\') . '\\' . $className;
    }