filebeat: fix check against nil

[florianl]

Signed-off-by: Florian Lehner [email protected]

What does this PR do?

This PR fixes bugs of incorrect checks.

Checklist

• [x] My code follows the style guidelines of this project
• [ ] ~~I have commented my code, particularly in hard-to-understand areas~~ no relevant code changes
• [ ] ~~I have made corresponding changes to the documentation~~ no relevant code changes
• [ ] ~~I have made corresponding change to the default configuration files~~ no relevant code changes
• [ ] ~~I have added tests that prove my fix is effective or that my feature works~~ existing tests cover the relevant changes
• [ ] ~~I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.~~ no relevant code changes

[mergify[bot]]

This pull request does not have a backport label. If this is a bug or security fix, could you label this PR @florianl? 🙏. For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[florianl]

Checked reported linting errors. They are not related to the proposed changes in this PR.

[elasticmachine]

:green_heart: Build Succeeded

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Build stats

• Start Time: 2022-09-15T07:35:55.159+0000

• Duration: 70 min 54 sec

Test stats :test_tube:

Test	Results
Failed	0
Passed	6857
Skipped	737
Total	7594

:green_heart: Flaky test report

Tests succeeded.

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[florianl]

friendly ping @belimawr

[florianl]

I don't have permission to merge this PR. @belimawr - maybe you can merge it?

Otherwise I will close this PR in a few days, if there is no interest.