code: func (iter *UnionIter) Close() {
  	if iter.snapshotIt != nil {
  		iter.snapshotIt.Close()
  		iter.snapshotIt = nil
  	}
  	if iter.dirtyIt != nil {
  		iter.dirtyIt.Close()
  		iter.dirtyIt = nil
  	}
  }
docs: // Close implements the Iterator Close interface.