Client 20.0.1 changes to non-required Map fields break basic use cases

[rjeberhard]

Describe the bug
The following example Java class results in an exception when run:

import io.kubernetes.client.openapi.ApiClient;
import io.kubernetes.client.openapi.ApiException;
import io.kubernetes.client.openapi.Configuration;
import io.kubernetes.client.openapi.apis.CoreV1Api;
import io.kubernetes.client.openapi.models.V1Container;
import io.kubernetes.client.openapi.models.V1ObjectMeta;
import io.kubernetes.client.openapi.models.V1Pod;
import io.kubernetes.client.openapi.models.V1PodSpec;
import io.kubernetes.client.util.Config;
import java.io.IOException;
import java.util.Arrays;

public class PodExample {
    public static void main(String[] args) throws IOException, ApiException {
        ApiClient client = Config.defaultClient();
        Configuration.setDefaultApiClient(client);

        CoreV1Api api = new CoreV1Api();
        api.createNamespacedPod("test-namespace",
            new V1Pod().metadata(new V1ObjectMeta().name("test-pod").namespace("test-namespace"))
                    .spec(new V1PodSpec().addContainersItem(
                            new V1Container().name("test-container").image("busybox:1.28")
                                    .command(Arrays.asList("sh", "-c", "echo \"Hello, Kubernetes\""))))).execute();
    }
}

Assuming that you've created the "test-namespace" namespace, the output is:

Exception in thread "main" io.kubernetes.client.openapi.ApiException: Message: 
HTTP response code: 403
HTTP response body: {"kind":"Status","apiVersion":"v1","metadata":{},"status":"Failure","message":"pods \"test-pod\" is forbidden: pod rejected: Pod Overhead set without corresponding RuntimeClass defined Overhead","reason":"Forbidden","details":{"name":"test-pod","kind":"pods"},"code":403}

HTTP response headers: {audit-id=[db4aab6c-a8c6-43c4-955d-bc49625c2548], cache-control=[no-cache, private], content-length=[272], content-type=[application/json], date=[Thu, 25 Apr 2024 19:24:02 GMT], x-kubernetes-pf-flowschema-uid=[190a5b0e-20ba-45d3-a8d8-5fdb90717772], x-kubernetes-pf-prioritylevel-uid=[655b2c69-cb8a-4115-a2b1-885c91d769a7]}
	at io.kubernetes.client.openapi.ApiClient.handleResponse(ApiClient.java:1116)
	at io.kubernetes.client.openapi.ApiClient.execute(ApiClient.java:1029)
	at io.kubernetes.client.openapi.apis.CoreV1Api.createNamespacedPodWithHttpInfo(CoreV1Api.java:10876)
	at io.kubernetes.client.openapi.apis.CoreV1Api.access$22100(CoreV1Api.java:77)
	at io.kubernetes.client.openapi.apis.CoreV1Api$APIcreateNamespacedPodRequest.execute(CoreV1Api.java:10972)
	at PodExample.main(PodExample.java:23)

Process finished with exit code 1

I believe the reason is that classes like V1PodSpec set non-required Map-typed fields to a new HashMap rather than leaving them as null.

We see similar unexpected behavior with Yaml.dump(). For instance, if you create a V1CustomResourceDefinition and populate a schema then Yaml.dump() will output fields like "definitions" and "dependencies" that are not legal to specify.

Client Version
e.g. 20.0.1

Kubernetes Version
e.g. 1.28.2

Java Version
e.g. Java 8

To Reproduce
Run the reproducer after creating the namespace.

Expected behavior
I'm hoping that these fields can be null by default as they were in 19.0.1.

KubeConfig
If applicable, add a KubeConfig file with secrets redacted.

Server (please complete the following information):

• OS: [e.g. MacOS]
• Environment [e.g. container]
• Cloud [e.g. Oracle OKE]

Additional context
Add any other context about the problem here.

[brendandburns]

This is a duplicate of #3076 closing in favor of that issue.

tl;dr; I think this is a bug in the upstream kubernetes api server.

[rjeberhard]

Thanks, @brendandburns. I'll put my thoughts over there. I'm going to argue in favor of not treating this as a bug in the upstream server and pushing for a fix in the template generation.