code: public static function getContentType(ResponseInterface $response): ?string
      {
          $contentTypes = $response->getHeader(HttpInterface::HEADER_CONTENT_TYPE);
          if (empty($contentTypes[0])) {
              return null;
          }
  
          if (false === strpos($contentTypes[0], ';')) {
              return $contentTypes[0];
          }
  
          return substr($contentTypes[0], 0, strpos($contentTypes[0], ';'));
      }
docs: @param ResponseInterface $response
  
  @return null|string