private function httpGet( $path, array $query = array() ){

        $url = new Uri( $this->baseUrl . $path );

        foreach( $query as $name => $value ){
            $url = Uri::withQueryValue($url, $name, $value );
        }

        //---

        $request = new Request(
            'GET',
            $url,
            $this->buildHeaders()
        );

        try {

            $response = $this->getHttpClient()->sendRequest( $request );

        } catch (\RuntimeException $e){
            throw new Exception\PostcodeException( $e->getMessage(), $e->getCode(), $e );
        }

        //---

        if( $response->getStatusCode() != 200 ){
            throw $this->createErrorException( $response );
        }

        return $response;

    }