code: public static InvocationStage makeStage(Object rv) {
        if (rv instanceof InvocationStage) {
           return (InvocationStage) rv;
        } else {
           return new SyncInvocationStage(rv);
        }
     }
docs: Encode the result of an {@link #invokeNext(InvocationContext, VisitableCommand)} in an {@link InvocationStage}.
  
  <p>May not create a new instance, if the result is already an {@code InvocationStage}.