code: func (s *MockStore) Get(key string) (*store.KVPair, error) {
  	mData := s.db[key]
  	if mData == nil {
  		return nil, nil
  	}
  	return &store.KVPair{Value: mData.Data, LastIndex: mData.Index}, nil
  
  }
docs: // Get the value at "key", returns the last modified index
  // to use in conjunction to CAS calls