Superfluous null checks introduced without explanation in f26ac66, probably in the course of debugging.
The elements of Jenkins.getComputers are guaranteed to be non-null,
and a separate change ought to assure that @StepContextParameter fields are set.
Better resolution of FB warning from 33656bf; align with future Jenkins.getActiveInstance.
5d4b42b copied RetryStep/config.jelly without modification.
After 7974824, StepExecution.getStepDescriptor is no longer used, so deleting it.
Rawtypes warning.
checkContextAvailability can be final.
ExecutorStepExecution does not supply a Launcher.
Missed a couple of implementations of getStepDescriptor.
Trying to diagnose random failures.
https://jenkins.ci.cloudbees.com/job/plugins/job/workflow-plugin/org.jenkins-ci.plugins.workflow$workflow-aggregator/572/testReport/junit/org.jenkinsci.plugins.workflow.steps.scm/GitStepTest/changelogAndPolling/
… org.jenkinsci.plugins.workflow.job.WorkflowRun finish
INFO: demo #1 completed: SUCCESS
… hudson.plugins.git.GitStatus$JenkinsAbstractProjectListener onNotifyCommit
INFO: Triggering the polling of demo
… hudson.triggers.SCMTrigger$Runner run
INFO: SCM changes detected in demo. Triggering  #2
java.lang.AssertionError: expected:<2> but was:<1>
	at …
	at org.jenkinsci.plugins.workflow.steps.scm.GitStepTest.changelogAndPolling(GitStepTest.java:110)