public function setGapImgs(GapImgCollection $gapImgs)
    {
        if (count($gapImgs) > 0) {
            $this->gapImgs = $gapImgs;
        } else {
            $msg = "A GraphicGapMatch interaction must composed of at least 1 GapImg object, none given.";
            throw new InvalidArgumentException($msg);
        }
    }