Can't decode nested field which parent field could be null or record

[Pyroarsonist]

I have next code:

package main

import (
	"log"

	"github.com/linkedin/goavro/v2"
)

const schema = `{
  "type": "record",
  "name": "Payload",
  "fields": [
    {
      "name": "image",
      "default": "null",
      "type": [
        "null",
        {
          "type": "record",
          "name": "Image",
          "fields": [
            {
              "name": "url",
              "type": "string"
            },
            {
              "name": "caption",
              "type": "string",
              "default": "undefined"
            }
          ]
        }
      ]
    }
  ]
}


`

func main() {
	codec, err := goavro.NewCodec(schema)
	if err != nil {
		println("schema is wrong")
		log.Fatalln(err)
	}

	str := `{"image": {"caption": "asd"}}`

	a, b, err := codec.NativeFromTextual([]byte(str))

	if err != nil {
		println(err.Error())
	} else {
		println(string(b))
		println(a)
	}

}

Image is optional field: it could be null or contain some fields (url and caption).

Instead of successful parsing of JSON i receving next error message: cannot decode textual record "SendPayload": cannot decode textual union: cannot decode textual map: cannot determine codec: "caption" for key: "image".

Problem is that avro schema contains image.caption field. I tried sending image with caption, url and both, but problem persists.

[dkus]

This works:

str := `{"image": { "Image" : {"caption": "asd", "url": "URL"}}}`

When using union type, target type should be specified