code: func (fn *ScriptFunction) Source() (interface{}, error) {
  	source := make(map[string]interface{})
  	if fn.script != nil {
  		src, err := fn.script.Source()
  		if err != nil {
  			return nil, err
  		}
  		source["script"] = src
  	}
  	// Notice that the weight has to be serialized in FunctionScoreQuery.
  	return source, nil
  }
docs: // Source returns the serializable JSON data of this score function.