[Bug] Cannot read field mbean because finalML is null #24410

### Search before reporting

- [x] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Read release policy

- [x] I understand that [unsupported versions](https://pulsar.apache.org/contribute/release-policy/#supported-versions) don't get bug fixes. I will attempt to reproduce the issue on a supported version of Pulsar client and Pulsar broker.

### User environment

version: 3.3.6

### Issue Description

I noticed that PR #14606 attempted to fix this issue but was closed with the note that it had already been addressed in PR #12103. However, after checking the code in Pulsar 3.3.6, I can confirm that the fix from PR #12103 is present, yet the issue still persists. This suggests that the previous fix may not have fully resolved the problem.

### Error messages

```text

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### Reproducing the issue

It's hard to reproduce it

### Additional information


### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

No file, test, or entry point is named. Start by reviewing the issue's references to PRs #14606 and #12103 and investigate the reported finalML-null mbean failure on Pulsar 3.3.6. Done means reproducing or isolating the failure and confirming that the null-field error is resolved.

Written by the indexing model from the issue text.