@Override public PollingResult poll(TaskListener listener) {
        // TODO call SCMPollListener
        WorkflowRun lastBuild = getLastBuild();
        if (lastBuild == null) {
            listener.getLogger().println("no previous build to compare to");
            // Note that we have no equivalent of AbstractProject.NoSCM because without an initial build we do not know if this project has any SCM at all.
            return Queue.getInstance().contains(this) ? PollingResult.NO_CHANGES : PollingResult.BUILD_NOW;
        }
        WorkflowRun perhapsCompleteBuild = getLastSuccessfulBuild();
        if (perhapsCompleteBuild == null) {
            perhapsCompleteBuild = lastBuild;
        }
        if (pollingBaselines == null) {
            pollingBaselines = new ConcurrentHashMap<String,SCMRevisionState>();
        }
        PollingResult result = PollingResult.NO_CHANGES;
        for (WorkflowRun.SCMCheckout co : perhapsCompleteBuild.checkouts(listener)) {
            if (!co.scm.supportsPolling()) {
                listener.getLogger().println("polling not supported from " + co.workspace + " on " + co.node);
                continue;
            }
            String key = co.scm.getKey();
            SCMRevisionState pollingBaseline = pollingBaselines.get(key);
            if (pollingBaseline == null) {
                pollingBaseline = co.pollingBaseline; // after a restart, transient cache will be empty
            }
            if (pollingBaseline == null) {
listener.getLogger().println("no polling baseline in " + co.workspace + " on " + co.node);

	@Override
	public SCMRevisionState calcRevisionsFromBuild(
			@Nonnull final Run<?, ?> build, @Nullable final FilePath workspace,
			@Nullable final Launcher launcher, @Nonnull final TaskListener listener
			) throws IOException, InterruptedException {
		// We add our SCMRevisionState from within checkout, so this shouldn't
		// be called often. However it will be called if this is the first
		// build, if a build was aborted before it reported the repository
		// state, etc.
		return null;
}