弹性：错误400（错误请求）：执行脚本失败[type = illegal_argument_exception]

Using gopkg.in/olivere/elastic.v5 for adding a field to a document in elasticsearch Code:

script := elastic.NewScript(`ctx._source.new_field += params.vijay`).Param("vijay", "kumar").p
                //script := elastic.NewScript("ctx._source.retweets += params.num").Param("num", 1)
                fmt.Println("script", script)
                update, err := client.Update().Index("idx001").Type("sdoc").Id(t.Docid).Script(script).Do(ctx)
                if err != nil {
                    // Handle error
                    panic(err)
                }
                fmt.Println("result is", update.Result)

And the result got is(here i am printing the script formed also)

script &{ctx._source.new_field += params.vijay map[vijay:kumar]} panic: elastic: Error 400 (Bad Request): failed to execute script [type=illegal_argument_exception]

Expected the field vijay to be added into elasticsearch with the value kumar