protected function &getMap(): array
    {
        if (!isset($this->map)) {
            $this->map = []; // Define.

            if (is_file($this->map_file)) {
                $this->map = file_get_contents($this->map_file);
                $this->map = json_decode($this->map, true);
                $this->map = is_array($this->map) ? $this->map : [];
            } // Only if file exists, otherwise empty array.
        }
        return $this->map;
    }