Some queries about nexus operation

Hi Temporal Team,

I got two questions regarding nexus operation:

  1. From the documentation Temporal Nexus - Java SDK Feature Guide | Temporal Platform Documentation. Looks like nexus operation can only be invoked from a caller workflow. Am I right about it?

  2. For the operation handler,
    public static <T, R> OperationHandler<T, R> fromWorkflowMethod(WorkflowMethodFactory<T, R> startMethod) {
    return new WorkflowRunOperationImpl((context, details, input) → {
    return WorkflowHandle.fromWorkflowMethod(startMethod.apply(context, details, input), input);
    });
    }
    How should i use it if my workflow method return is void but not java.lang.Void

Best regards,
Jx