我有一段代码：

List<ProcessInstance> instances =
                    processEngine.getRuntimeService().createProcessInstanceQuery().processInstanceId(processInstanceId).list();
instances.forEach(this::listProcessInstance);
    private void listProcessInstance (ProcessInstance processInstance) {
                log.info("<-------------- ProcessInstance ---------------> {} ", processInstance);
                log.info(String.valueOf(processInstance.getProcessVariables()));
                log.info("<-------------- ProcessInstance --------------->");
        }

其中processvariables为空，但在表上有以下信息：

select * from ACT_RU_VARIABLE where PROC_INST_ID_ = 76759;