code: func (hook *GraylogHook) Blacklist(b []string) {
  	hook.blacklist = make(map[string]bool)
  	for _, elem := range b {
  		hook.blacklist[elem] = true
  	}
  }
docs: // Blacklist create a blacklist map to filter some message keys.
  // This useful when you want your application to log extra fields locally
  // but don't want graylog to store them.