code: func validateNotifier(c *validation.Context, cfgNotifier *notifypb.Notifier, builderNames stringset.Set) {
  	for i, cfgNotification := range cfgNotifier.Notifications {
  		c.Enter("notification #%d", i+1)
  		validateNotification(c, cfgNotification)
  		c.Exit()
  	}
  	for i, cfgBuilder := range cfgNotifier.Builders {
  		c.Enter("builder #%d", i+1)
  		validateBuilder(c, cfgBuilder, builderNames)
  		c.Exit()
  	}
  }
docs: // validateNotifier validates a Notifier.