src/BaseResponse.php
public function withHeader($header = null, $value = null) {
        $this->validateResponse();
        return $this->response->withHeader($header, $value);
    }
public function withHeader($header = null, $value = null) {
        $this->validateResponse();
        return $this->response->withHeader($header, $value);
    }
@param null $header
@param null $value

@return \GuzzleHttp\Psr7\MessageTrait
@throws \Exception