pentium100 opened a new issue, #4100:
URL: https://github.com/apache/hertzbeat/issues/4100
### Is there an existing issue for this?
- [x] I have searched the existing issues
### Current Behavior
[BUG] 当修改一个使用了服务发现的监控时，后台会抛异常
2026-03-29 15:22:10 [http-nio-1157-exec-1] ERROR
org.apache.hertzbeat.manager.support.GlobalExceptionHandler -
[monitor]-[unknown error happen]-null
java.lang.NullPointerException
at java.base/java.util.Objects.requireNonNull(Objects.java:220)
at
java.base/java.util.ImmutableCollections$MapN.<init>(ImmutableCollections.java:1437)
at java.base/java.util.Map.of(Map.java:1384)
at
org.apache.hertzbeat.manager.service.impl.MonitorServiceImpl.modifyMonitor(MonitorServiceImpl.java:418)
at
java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)
at
org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:359)
at
org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
新建时不会，就是修改会。原因是修改的服务上没有处理scrape为service discovery时，instance为空的情况。
### Expected Behavior
_No response_
### Steps To Reproduce
1. add any type of monitor
2. select nacos service discovery
3. fill nacos server information.
4. confirm it.
5. edit monitor.
6. don't change any thing , just save it.
7. you will got error.
### Environment
```markdown
HertzBeat version(s): v1.8.0
```
### Debug logs
_No response_
### Anything else?
_No response_
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