code: func (tx *Tx) Get(key string, ignoreExpired ...bool) (val string, err error) {
  	if tx.db == nil {
  		return "", ErrTxClosed
  	}
  	var ignore bool
  	if len(ignoreExpired) != 0 {
  		ignore = ignoreExpired[0]
  	}
  	item := tx.db.get(key)
  	if item == nil || (item.expired() && !ignore) {
  		// The item does not exists or has expired. Let's assume that
  		// the caller is only interested in items that have not expired.
  		return "", ErrNotFound
  	}
  	return item.val, nil
  }
docs: // Get returns a value for a key. If the item does not exist or if the item
  // has expired then ErrNotFound is returned. If ignoreExpired is true, then
  // the found value will be returned even if it is expired.