code: public function checkHeaders(HeaderParametersInterface $parameters)
      {
          // Note: for these checks the order is specified by spec. See details inside.
  
          $this->checkAcceptHeader($parameters);
  
          // clients must send content type only if the request has body so there is no point in checking
          // `Content-Type` header if the original request is bodiless.
          if ($parameters->getContentTypeHeader() !== null) {
              $this->checkContentTypeHeader($parameters);
          }
      }
docs: @param HeaderParametersInterface $parameters
  
  @return void