code: func NewDNSProviderConfig(config *Config) (*DNSProvider, error) {
  	if config == nil {
  		return nil, errors.New("ns1: the configuration of the DNS provider is nil")
  	}
  
  	if config.APIKey == "" {
  		return nil, fmt.Errorf("ns1: credentials missing")
  	}
  
  	client := rest.NewClient(config.HTTPClient, rest.SetAPIKey(config.APIKey))
  
  	return &DNSProvider{client: client, config: config}, nil
  }
docs: // NewDNSProviderConfig return a DNSProvider instance configured for NS1.