public function setCustom($dimension, $value = null)
    {
        if ($value === null && is_array($dimension)) {
            $params = json_encode($dimension);
            $trackingCode = "ga('set', $params);";
        } else {
            $trackingCode = "ga('set', '$dimension', '$value');";
        }

        $this->trackCustom($trackingCode);

        return $this;
    }