code: func (db *DB) Exists(key []byte) (int64, error) {
  	if err := checkKeySize(key); err != nil {
  		return 0, err
  	}
  
  	var err error
  	key = db.encodeKVKey(key)
  
  	var v []byte
  	v, err = db.bucket.Get(key)
  	if v != nil && err == nil {
  		return 1, nil
  	}
  
  	return 0, err
  }
docs: // Exists check data exists or not.