def set(value)
    if value.nil?
      @is_nil = true
      @data = nil
      _set(nil)
    else
      @is_nil = false
      _set(screen_data(value))
    end
  end
def set(value)
    if value.nil?
      @is_nil = true
      @data = nil
      _set(nil)
    else
      @is_nil = false
      _set(screen_data(value))
    end
  end
set accepts a string which follows lexical space (ex. String: "+123"), or
 an object which follows canonical space (ex. Integer: 123).