How to use the @0x/asset-swapper.SwapQuoterError.AssetUnavailable function in @0x/asset-swapper

? Web3Wrapper.toUnitAmount(error.amountAvailableToFill, asset.metaData.decimals)
                        : error.amountAvailableToFill;
                const roundedUnitAmountAvailableToFill = unitAmountAvailableToFill.decimalPlaces(
                    2,
                    BigNumber.ROUND_DOWN,
                );

                if (roundedUnitAmountAvailableToFill.isGreaterThan(BIG_NUMBER_ZERO)) {
                    return `There are only ${roundedUnitAmountAvailableToFill} ${assetName} available to buy`;
                }
            }

            return `Not enough ${assetName} available`;
        } else if (
            error.message === SwapQuoterError.StandardRelayerApiError ||
            error.message.startsWith(SwapQuoterError.AssetUnavailable)
        ) {
            const assetName = assetUtils.bestNameForAsset(asset, 'This asset');
            return `${assetName} is currently unavailable`;
        }

        return undefined;
    },
};