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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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