code: func (k *Store) Get(key string) interface{} {
  	// Read-only lock
  	k.mu.RLock()
  	defer k.mu.RUnlock()
  
  	// zero value of interface{} is nil so this does what we want
  	return k.db[key]
  }
docs: // Get retrieves a value from the store, or nil if it is not present