docs: def update_note(note_id: NoteId, body: Body=None, done: Done=None) -> Note:
      """Update an existing note."""
      if note_id != 1:
          raise NotFoundError('Note does not exist')
      new_note = note.copy()
      if body is not None:
          new_note['body'] = body
      if done is not None:
          new_note['done'] = done
      return new_note