[Bug]: 定义变量但不引用导致的运行时异常

[Jiakaic]

Version

main branch

Component

API (Backend)

Bug Description

例：结束节点定义一个变量但不引用，运行时会异常

Steps to Reproduce

增加一个结束节点，定义一个变量且不引用

Expected Behavior

提示引用为空而不是透传后端堆栈

Environment

ignore

Error Logs

Additional Context

No response