ERC721XTokenNFT.sol modification for tokenType mapping

ERC721XTokenNFT

mapping(uint256 => uint256) tokenType;

uint256 constant NFT = 1;
uint256 constant FT = 2;

/**
 * @dev Returns whether the specified token exists
 * @param _tokenId uint256 ID of the token to query the existence of
 * @return whether the token exists
 */
function exists(uint256 _tokenId) public view returns (bool) {
  // address owner = tokenOwner[_tokenId];
  // return owner != address(0);
  return tokenType[_tokenId] != 0;
}

function _mint(uint256 _tokenId, address _to) internal {
  require(!exists(_tokenId), "Error: Tried to mint duplicate token id");
  _updateTokenBalance(_to, _tokenId, 1, ObjectLib.Operations.REPLACE);
  tokenOwner[_tokenId] = _to;
  tokenType[_tokenId] = NFT;
  allTokens.push(_tokenId);
  emit Transfer(address(this), _to, _tokenId);
}