code: func (f *QueryStringFilter) MarshalJSON() ([]byte, error) {
  	root := map[string]interface{}{
  		"query_string": map[string]interface{}{
  			"query":            f.Query,
  			"analyze_wildcard": f.AnalyzeWildcard,
  		},
  	}
  
  	return json.Marshal(root)
  }
docs: // MarshalJSON returns the JSON encoding of the query string filter.