public function build(array $data = [])
    {
        if(!$this->oAuth2Credential)
            $this->oAuth();

        $data = $this->mergeData($data);

        $adwordsSession = new AdWordsSessionBuilder();

        return $adwordsSession->withDeveloperToken($data['developerToken'])
                ->withClientCustomerId($data['clientCustomerId'])
                ->withOAuth2Credential($this->oAuth2Credential)
                ->build();
    }