code: public function isMultipart(HttpHeaders $headers): bool
      {
          $contentType = null;
          $headers->tryGetFirst('Content-Type', $contentType);
  
          return preg_match("/multipart\//i", $contentType) === 1;
      }
docs: Gets whether or not the message is a multipart message
  
  @param HttpHeaders $headers The headers to parse
  @return bool True if the request is a multipart message, otherwise false
  @throws RuntimeException Thrown if the content type header's hash key could not be calculated