function _collateralPriceUsd() internal view returns (uint256) {
        int256 answer = oracle.latestAnswer();
        uint8 decimals = oracle.decimals();

        require(answer > 0, "invalid_oracle_answer");

        ...
function _collateralPriceUsd() internal view returns (uint256) {

(uint80 roundID, int256 answer, , uint256 timestamp, uint80 answeredInRound) = oracle.latestRoundData();
   
    require(answer > 0, "invalid_oracle_answer");
    require(answeredInRound >= roundID, "ChainLink: Stale price");
    require(timestamp > 0, "ChainLink: Round not complete");

         ...
