code: func (db *Database) Put(key []byte, value []byte) error {
  	db.lock.Lock()
  	defer db.lock.Unlock()
  
  	if db.db == nil {
  		return errMemorydbClosed
  	}
  	db.db[string(key)] = common.CopyBytes(value)
  	return nil
  }
docs: // Put inserts the given value into the key-value store.