code: private static function createDefaultBoundary(): string
      {
          try {
              // The following creates a UUID v4
              $string = random_bytes(16);
              $string[6] = chr(ord($string[6]) & 0x0f | 0x40);
              $string[8] = chr(ord($string[8]) & 0x3f | 0x80);
  
              return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($string), 4));
          } catch (Exception $ex) {
              throw new RuntimeException('Failed to generate random bytes', 0, $ex);
          }
      }
docs: Creates the default boundary in case one wasn't specified
  
  @return string The default boundary
  @throws RuntimeException Thrown if random bytes could not be generated