code: function toStorageRequest(bid) {
    const vastValue = bid.vastXml ? bid.vastXml : wrapURI(bid.vastUrl, bid.vastImpUrl);
    let payload = {
      type: 'xml',
      value: vastValue,
      ttlseconds: Number(bid.ttl)
    };
  
    if (typeof bid.customCacheKey === 'string' && bid.customCacheKey !== '') {
      payload.key = bid.customCacheKey;
    }
  
    return payload;
  }
docs: Wraps a bid in the format expected by the prebid-server endpoints, or returns null if
  the bid can't be converted cleanly.
  
  @param {CacheableBid} bid