public function setBccSettings($enable, $email = null)
    {
        if ($enable instanceof BccSettings) {
            $bcc = $enable;
            $this->bcc = $bcc;
            return;
        }
        if (!is_bool($enable)) {
            throw new TypeException(
                '$enable must be an instance of SendGrid\Mail\BccSettings or of type bool.'
            );
        }
        $this->bcc = new BccSettings($enable, $email);
    }