Cherry-pick #24760 to 7.x: Fix nil pointer for nil list item

[michalpristas]

Cherry-pick of PR #24760 to 7.x branch. Original message:

What does this PR do?

This PR guards against a nil items which are part of the list. Fn call then casues agent to panic.

Why is it important?

Fixes: #23734

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Build stats

• Build Cause: Pull request #24765 opened

• Start Time: 2021-03-25T14:49:27.098+0000

• Duration: 69 min 1 sec

• Commit: 531e5c3

Test stats 🧪

Test	Results
Failed	0
Passed	6532
Skipped	24
Total	6556

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Test stats 🧪

Test	Results
Failed	0
Passed	6532
Skipped	24
Total	6556