code: func (s *GlobalStore) Get(addr common.Address, key []byte) (data []byte, err error) {
  	s.mu.RLock()
  	defer s.mu.RUnlock()
  
  	if _, has := s.nodeKeyIndex(addr, key); !has {
  		return nil, mock.ErrNotFound
  	}
  
  	data, ok := s.data[string(key)]
  	if !ok {
  		return nil, mock.ErrNotFound
  	}
  	return data, nil
  }
docs: // Get returns chunk data if the chunk with key exists for node
  // on address addr.