code: func (f *Folder) FindFolder(name string) (tree.Tree, error) {
  	sub := f.findFolder(strings.Split(strings.TrimSuffix(name, sep), sep))
  	if sub == nil {
  		return nil, errors.Errorf("Entry not found")
  	}
  	return sub, nil
  }
docs: // FindFolder returns a sub-tree or nil, if the subtree does not exist