Fix ExtractItems to preserve empty maps and lists

[mrIncompetent]

What

ExtractItems now preserves empty maps and lists ({} and []) instead of converting them to null.

Why

The apply config that gets applied should be the same that gets later extracted. Today this isn't the case for empty, non-nil, fields (like volumes[].emptyDir).

Changes

• Modified typed/remove.go to preserve empty maps and lists during extraction
• Added test cases for empty maps and lists (nil and non-nil)

Additional

Attached a test case that uses the Pod apply config as a more specific example

package pdb

import (
	"encoding/json"
	"testing"

	"github.com/stretchr/testify/require"
	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	corev1apply "k8s.io/client-go/applyconfigurations/core/v1"
	"k8s.io/client-go/kubernetes/fake"
)

var (
	desiredApplyConf = corev1apply.Pod("test", "default").WithSpec(corev1apply.PodSpec().
		WithContainers(
			corev1apply.Container().
				WithName("main").
				WithImage("nginx:latest").
				WithVolumeMounts(
					corev1apply.VolumeMount().
						WithName("data").
						WithMountPath("/data"),
				),
		).
		WithVolumes(
			corev1apply.Volume().
				WithName("data").
				WithEmptyDir(corev1apply.EmptyDirVolumeSource()),
		))
)

func Test_ExtractPod(t *testing.T) {
	client := fake.NewClientset()
	pod, err := client.CoreV1().Pods("default").Apply(t.Context(), desiredApplyConf, v1.ApplyOptions{FieldManager: "test"})
	require.NoError(t, err)

	extractedApplyConf, err := corev1apply.ExtractPod(pod, "test")
	require.NoError(t, err)

	extractedJSON, err := json.Marshal(extractedApplyConf)
	require.NoError(t, err)
	t.Logf("Extracted Pod Apply Config: \n%s", string(extractedJSON))
	desiredJSON, err := json.Marshal(desiredApplyConf)
	require.NoError(t, err)
	t.Logf("Desired Pod Apply Config: \n%s", string(desiredJSON))

	require.JSONEq(t, string(desiredJSON), string(extractedJSON), "extracted apply config does not match the desired one")
}

[k8s-ci-robot]

Hi @mrIncompetent. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[mrIncompetent]

Ping @jpbetz

[jpbetz]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jpbetz, mrIncompetent

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