After the upgrade my build breaks with a cryptic NullPointerException error:

[PostBuildScript] - [INFO] Executing post build scripts.
ERROR: Build step failed with exception
java.lang.NullPointerException
at org.jenkinsci.plugins.postbuildscript.processor.Processor.processScriptFiles(Processor.java:110)
at org.jenkinsci.plugins.postbuildscript.processor.Processor.processScripts(Processor.java:89)
at org.jenkinsci.plugins.postbuildscript.processor.Processor.process(Processor.java:79)
at org.jenkinsci.plugins.postbuildscript.processor.Processor.process(Processor.java:73)
at org.jenkinsci.plugins.postbuildscript.PostBuildScript.perform(PostBuildScript.java:77)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:803)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:752)
at hudson.model.Build$BuildExecution.post2(Build.java:177)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:697)
at hudson.model.Run.execute(Run.java:1932)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:429)
Build step 'Execute scripts' marked build as failure
An attempt to send an e-mail to empty list of recipients, ignored.
Notifying upstream projects of job completion
Finished: FAILURE

All I did was to upgrade the postbuildscript plugin only. My Job DSL configuration did not change at all:

job.with {
publishers {
postBuildScripts {
steps {
shell(""" 

echo 'Hello world'

""".stripIndent())
}
onlyIfBuildSucceeds(false)
}
}
}

In the version 2.11.0, this Job DSL config produced the job output in image "correct-job-output.png", in 3.0.0 it produces the job output in image "broken-job-output.png".