code: func EncodeCMSketchWithoutTopN(c *CMSketch) ([]byte, error) {
  	if c == nil {
  		return nil, nil
  	}
  	p := CMSketchToProto(c)
  	p.TopN = nil
  	protoData, err := p.Marshal()
  	return protoData, err
  }
docs: // EncodeCMSketchWithoutTopN encodes the given CMSketch to byte slice.
  // Note that it does not include the topN.