code: func (mvcc *MVCCLevelDB) RawPut(key, value []byte) {
  	mvcc.mu.Lock()
  	defer mvcc.mu.Unlock()
  
  	if value == nil {
  		value = []byte{}
  	}
  	terror.Log(mvcc.db.Put(key, value, nil))
  }
docs: // RawPut implements the RawKV interface.