code: func NewGuard() *Guard {
  	lock.Lock()
  	defer lock.Unlock()
  
  	if current != nil {
  		return current
  	}
  
  	current = &Guard{
  		secrets: []*Secret{},
  		lock:    &sync.Mutex{},
  	}
  
  	return current
  }
docs: // NewGuard returns a Guard instance or errors if a guard already exists.