public function getHash($fileName)
    {
        if (array_key_exists($fileName, $this->data)) {
            return $this->data[$fileName];
        } else if (array_key_exists($this->_makeRelative($fileName), $this->data)) {
            return $this->data[$this->_makeRelative($fileName)];
        } else {
            return null;
        }
    }