public function save($filename = null, $jsonFlag = JSON_UNESCAPED_SLASHES)
    {
        if ($filename === null) {
            if ($this->outFileName === null) {
                throw new OutFileNotSpecified();
            }
            $filename = $this->outFileName;
        }
        IO::saveJSON($this->getData(), $filename, $jsonFlag);
        $this->outFileName = $filename;
    }