public function getChartByIndex($index = null)
    {
        $chartCount = count($this->chartCollection);
        if ($chartCount == 0) {
            return false;
        }
        if (is_null($index)) {
            $index = --$chartCount;
        }
        if (!isset($this->chartCollection[$index])) {
            return false;
        }

        return $this->chartCollection[$index];
    }