code: func getConfiguredCredentialStore(c *ConfigFile, registryHostname string) string {
  	if c.CredentialHelpers != nil && registryHostname != "" {
  		if helper, exists := c.CredentialHelpers[registryHostname]; exists {
  			return helper
  		}
  	}
  	return c.CredentialsStore
  }
docs: // getConfiguredCredentialStore returns the credential helper configured for the
  // given registry, the default credsStore, or the empty string if neither are
  // configured.