func (s *MergeIterator) Key() []byte {
	if len(s.h) == 0 {
		return nil
	}
	return s.h[0].itr.Key()
}
func (s *MergeIterator) Key() []byte {
	if len(s.h) == 0 {
		return nil
	}
	return s.h[0].itr.Key()
}
func ( s * MergeIterator ) Key ( ) [ ] byte { if len ( s . h ) == 0 { return nil } return s . h [ 0 ] . itr . Key ( ) }
// Key returns the key associated with the current iterator
Key returns the key associated with the current iterator