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