Using `edit add label` with the `--without-selector` flag without pre-existing labels causes an error

[DGoldfayn]

What happened?

When using:

kustomize --stack-trace edit add label --without-selector test1:a test2:b

On a kustomization.yaml without pre-existing

labels:
  - pairs:
      environment: dev

causes the following error:

Error: label test2 already in kustomization file. Use --force to override.

IMPORTANT:

The following permutations allow it to work:

• Use the --force flag
• Omit the --without-selector flag
• Have pre-existing labels in the kustomization.yaml (see above)

What did you expect to happen?

The labels should be added like so:

labels:
- pairs:
    test1: a
    test2: b

How can we reproduce it (as minimally and precisely as possible)?

# kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- resources.yaml

# resources.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: test-object
data:
  placeholder: data

You can omit resources.yaml the error happens on an empty kustomization file too.

Expected output

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- resources.yaml
labels:
- pairs:
    test1: a
    test2: b

Actual output

Error: label test2 already in kustomization file. Use --force to override.

Kustomize version

5.7.1

Operating system

Linux

[isarns]

Created a PR to fix it #5991

[koba1t]

/triage accepted