function getTuber(uint256 _tokenId) public view returns (
    string tuberName,
    uint256 sellingPrice,
    address owner
  ) {
    Tuber storage tuber = tubers[_tokenId];
    tuberName = tuber.name;
    sellingPrice = tuberIndexToPrice[_tokenId];
    owner = tuberIndexToOwner[_tokenId];
  }