[hotfix] ftp writer format null

[chenghb606]

Purpose of this pull request

Which issue you fix

Fixes # (issue).

Checklist:

• [ ] I have executed the 'mvn spotless:apply' command to format my code.
• [ ] I have a meaningful commit message (including the issue id, the template of commit message is '[label-type-#issue-id][fixed-module] a meaningful commit message.')
• [ ] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have made corresponding changes to the documentation.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] New and existing unit tests pass locally with my changes.
• [ ] I have checked my code and corrected any misspellings.
• [ ] My commit is only one. (If there are multiple commits, you can use 'git squash' to compress multiple commits into one.)

[FlechazoW]

Please modify the code, and we will merge it.

[FlechazoW]

If the error is still not closed, you need to close in the finally block.

Please modify the code, and we will merge it.