ListTagsForResourceOutput.NextMarker with empty string

[anton-yurchenko]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone though Developer Guide and API reference
• I've checked AWS Forums and StackOverflow for answers
• I've searched for previous similar issues and didn't find any solution

Describe the bug
ListTagsForResource return NextMarker as empty string instead of nil.

I have a single CloudFront WAF IP Set which I am trying to retrieve with ListTagsForResource and I expect NextMarker to return nil as described here but instead it returns as empty string and causes the following error on next iteration:

InvalidParameter: 1 validation error(s) found.
- minimum field size of 1, ListTagsForResourceInput.NextMarker.

P.S: just in case this may collide somehow, I have some IP match conditions on "classic" (v1) WAF

Version of AWS SDK for Go?

1.34.13

Version of Go (go version)?

go version go1.14.2 darwin/amd64

To Reproduce (observed behavior)

package main

import (
	"fmt"
	"os"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/wafv2"
)

func main() {
	s := session.Must(session.NewSession())
	cli := wafv2.New(s)

	var token *string
	for {
		o, err := cli.ListTagsForResource(&wafv2.ListTagsForResourceInput{
			Limit:       aws.Int64(1),
			ResourceARN: aws.String("arn:aws:wafv2:us-east-1:<account-id>:global/ipset/<ipset-name>/<ipset-id>"),
			NextMarker:  token,
		})
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		if o.NextMarker != nil {
			token = o.NextMarker
			fmt.Printf("-> next marker: '%v'\n", *o.NextMarker)
		} else {
			break
		}
	}
}

-> next marker: ''
InvalidParameter: 1 validation error(s) found.
- minimum field size of 1, ListTagsForResourceInput.NextMarker.

exit status 1

Expected behavior
NextMarker should be returned only if there are more resources to retrieve, otherwise nil.

Quote from docs:

When you request a list of objects with a Limit setting, if the number of objects that are still available for retrieval exceeds the limit, AWS WAF returns a NextMarker value in the response.

[skotambkar]

We do not have plans to fix this in V1 SDK. The aws/aws-sdk-go-v2 has fixed this issue.

[github-actions]

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