code: func (f *Folder) addFile(path []string, contentType string) error {
  	if len(path) < 1 {
  		return errors.Errorf("Path must not be empty")
  	}
  	name := path[0]
  	if len(path) == 1 {
  		if _, found := f.Files[name]; found {
  			return errors.Errorf("File %s exists", name)
  		}
  		f.Files[name] = &File{
  			Name: name,
  			Metadata: map[string]string{
  				"Content-Type": contentType,
  			},
  		}
  		return nil
  	}
  	next := f.getFolder(name)
  	return next.addFile(path[1:], contentType)
  }
docs: // addFile adds new file