public function getDistance(int $point1 = null, int $point2 = null)
{
    $message = "В аргументах указаны несуществующие точки";

    if (isset($this->points[$point1]) && isset($this->points[$point2])) {
        $p1 = $this->points[$point1];
        $p2 = $this->points[$point2];

        return sqrt((float) (
            pow(($p2[0] - $p1[0]), 2) +
            pow(($p2[1] - $p1[1]), 2)
        ));
    }

    return $message;
}