code: func (itr *nsIterator) Next() (QueryResult, error) {
  	if itr.nextIndex >= itr.lastIndex {
  		return nil, nil
  	}
  	key := itr.sortedKeys[itr.nextIndex]
  	vv := itr.nsUpdates.m[key]
  	itr.nextIndex++
  	return &VersionedKV{CompositeKey{itr.ns, key}, VersionedValue{vv.Value, vv.Metadata, vv.Version}}, nil
  }
docs: // Next gives next key and versioned value. It returns a nil when exhausted