public void setWorkflowDefinition(Object workflowDef) {
        if (!(workflowDef == null || workflowDef instanceof WorkflowDef)) {
            throw new IllegalArgumentException(
                    "workflowDefinition must be either null or WorkflowDef");
        }
        this.workflowDefinition = workflowDef;
    }
@param workflowDef the workflowDefinition to set
common/src/main/java/com/netflix/conductor/common/metadata/workflow/SubWorkflowParams.java