code: func (u *URI) UnmarshalJSON(data []byte) error {
  	// Ignore null, like in the main JSON package.
  	if string(data) == "null" {
  		return nil
  	}
  	var s string
  	err := json.Unmarshal(data, &s)
  	if err != nil {
  		return err
  	}
  	u.URL, err = url.Parse(s)
  	return err
  }
docs: // UnmarshalJSON implements the json.Unmarshaler interface.
  // The URI is expected to be a quoted string.