public function move($filename, $pathTo, $pathFrom = null)
    {
        if ($pathFrom==null) {
            $pathFrom=$this->_filePath;
        }
        if (file_exists($pathFrom."/".$filename)) {
            $this->createDir($pathTo);
            return rename($pathFrom."/".$filename, $pathTo."/".$filename);
        } else {
            return null;
        }
    }