How to use the teraslice.saveAsset function in teraslice

await Promise.map(idArray, async (assetIdentifier) => {
            const downloaded = await fs.pathExists(path.join(assetsDirectory, assetIdentifier));
            // need to return the id to the assets array sent back
            if (downloaded) return { id: assetIdentifier };

            const assetRecord = await this.assetStore.get(assetIdentifier);
            logger.info(`loading assets: ${assetIdentifier}`);
            const buff = Buffer.from(assetRecord.blob, 'base64');
            return saveAsset(logger, assetsDirectory, assetIdentifier, buff);
        });