code: func (t *SecureTrie) TryUpdate(key, value []byte) error {
  	hk := t.hashKey(key)
  	err := t.trie.TryUpdate(hk, value)
  	if err != nil {
  		return err
  	}
  	t.getSecKeyCache()[string(hk)] = common.CopyBytes(key)
  	return nil
  }
docs: // TryUpdate associates key with value in the trie. Subsequent calls to
  // Get will return value. If value has length zero, any existing value
  // is deleted from the trie and calls to Get will return nil.
  //
  // The value bytes must not be modified by the caller while they are
  // stored in the trie.
  //
  // If a node was not found in the database, a MissingNodeError is returned.