code: func (s *GlobalStore) Get(addr common.Address, key []byte) (data []byte, err error) {
  	has, err := s.db.Has(indexForHashesPerNode(addr, key), nil)
  	if err != nil {
  		return nil, mock.ErrNotFound
  	}
  	if !has {
  		return nil, mock.ErrNotFound
  	}
  	data, err = s.db.Get(indexDataKey(key), nil)
  	if err == leveldb.ErrNotFound {
  		err = mock.ErrNotFound
  	}
  	return
  }
docs: // Get returns chunk data if the chunk with key exists for node
  // on address addr.