getMPUBucket(destinationBucket, bucketName, log, cb) {
        assert.strictEqual(typeof bucketName, 'string');
        const MPUBucketName = `${constants.mpuBucketPrefix}${bucketName}`;
        metadata.getBucket(MPUBucketName, log, (err, bucket) => {
            if (err?.is?.NoSuchBucket) {
                log.trace('no buckets found');
                const creationDate = new Date().toJSON();
                const mpuBucket = new BucketInfo(MPUBucketName,
                    destinationBucket.getOwner(),
                    destinationBucket.getOwnerDisplayName(), creationDate,
                    BucketInfo.currentModelVersion());
                // Note that unlike during the creation of a normal bucket,
                // we do NOT add this bucket to the lists of a user's buckets.
                // By not adding this bucket to the lists of a user's buckets,
                // a getService request should not return a reference to this
                // bucket.  This is the desired behavior since this should be
                // a hidden bucket.
                return metadata.createBucket(MPUBucketName, mpuBucket, log,
                    err => {
                        if (err) {
                            log.error('error from metadata', { error: err });
                            return cb(err);
                        }
                        return cb(null, mpuBucket);
                    });
            }
            if (err) {
                log.error('error from metadata', {
                    error: err,
                    method: 'services.getMPUBucket',
                });
                return cb(err);
            }
            return cb(null, bucket);
        });
    }
Gets the special multipart upload bucket associated with
the user's account or creates it if it does not exist
@param {Bucket} destinationBucket - bucket the mpu will end up in
@param {string} bucketName - name of the destination bucket
@param {object} log - Werelogs logger
@param {function} cb - callback that returns multipart
                       upload bucket or error if any
@return {undefined}