code: public void validate(boolean isOnlineExecution) throws MojoExecutionException {
      Set<String> unknownIds = Sets.newHashSet();
      Iterable<WorkflowStep> stepsToCheck = Iterables
          .unmodifiableIterable(Iterables.concat(this.workflow.getProcessingSteps(), this.workflow.getFinallySteps()));
      for (WorkflowStep workflowStep : stepsToCheck) {
        if (workflowStep.isParallel()) {
          ParallelWorkflowStep parallelWorkflowStep = (ParallelWorkflowStep) workflowStep;
          for (SimpleWorkflowStep simpleWorkflowStep : parallelWorkflowStep.getSteps()) {
            CDIMojoProcessingStep step = this.processingSteps.get(simpleWorkflowStep.getStepId());
            if (step == null) {
              unknownIds.add(simpleWorkflowStep.getStepId());
            } else {
              verifyOnlineStatus(step, isOnlineExecution);
            }
          }
        } else {
          SimpleWorkflowStep simpleWorkflowStep = (SimpleWorkflowStep) workflowStep;
          CDIMojoProcessingStep step = this.processingSteps.get(simpleWorkflowStep.getStepId());
          if (step == null) {
            unknownIds.add(simpleWorkflowStep.getStepId());
          } else {
            verifyOnlineStatus(step, isOnlineExecution);
          }
        }
      }
  
      if (!unknownIds.isEmpty()) {
        throw new MojoExecutionException(
            "There are no implementations for the following processing step ids specified in the workflow: "
                + Joiner.on(',').join(unknownIds));
      }
    }
docs: Performs a validation of the workflow with respect to the configured set of processing steps this plugin provides.
  <br>
  It is verified that each workflow step has a corresponding implementation providing the same step-id as specified
  in the workflow.
  
  @param isOnlineExecution whether Maven is executed in online mode or not.
  @throws MojoExecutionException if there are missing processing step implementations for one or more ids of the
  workflow. The exception message will list all missing ids.