public function setFileClassname($classname = null)
    {
        if ($classname === null) {
            $this->fileClass = null;
        }
        elseif ( ! class_exists($classname)) {
            throw ClassDoesNotExistException::create($classname);
        }
        else {
            $this->fileClass = (string) $classname;
        }
        return $this;
    }