[JENKINS-60517] Add null check for containerWorkingDirFilePath

[narayanan]

NPE happens when shell command gets executed inside a dynamically created container inside a DIND container. As this shell command is getting executed with in a container created outside of kubernetes pod, container working directory is getting set to null. Added a null check to avoid NPE.

Check https://issues.jenkins-ci.org/browse/JENKINS-60517 for more details

[k2glyph]

java.lang.NullPointerException
	at org.csanchez.jenkins.plugins.kubernetes.pipeline.ContainerExecDecorator$1.launch(ContainerExecDecorator.java:267)
	at hudson.Launcher$ProcStarter.start(Launcher.java:455)
	at hudson.Launcher$ProcStarter.join(Launcher.java:466)
	at org.jenkinsci.plugins.docker.commons.impl.RegistryKeyMaterialFactory.materialize(RegistryKeyMaterialFactory.java:101)
	at org.jenkinsci.plugins.docker.workflow.AbstractEndpointStepExecution2.doStart(AbstractEndpointStepExecution2.java:53)
	at org.jenkinsci.plugins.workflow.steps.GeneralNonBlockingStepExecution.lambda$run$0(GeneralNonBlockingStepExecution.java:77)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

[narayanan]

@k2glyph This is the same exception reported in the jenkins issue which was addressed as part of this PR. Do you still see the issue with the changes in this PR? If so, a sample JenkinsFile to reproduce the issue would help reproducing the issue.

[jglick]

This is currently failing for me locally in Microk8s (noticed while testing #1083); the build fails in docker run with

docker: Error response from daemon: cgroups: cgroup mountpoint does not exist: unknown.

Perhaps because Microk8s is now using cgroup v2, and docker:19-dind is assuming v1? Need to figure out how to Assume that the environment is capable of running DinD pods, at least with the specified image version.

[jglick]

Also failing locally when I run tests in #1275, but apparently not in CI.