Fix deprecation check failing on nil values

What does this MR do and why?

This backports !8616 (merged) to 18-2-stable-ee.

This commit fixes a regression in GitLab 18.2 due to !8470 (merged). Previously a blank default version were provided to check_config. Now the value can be nil if the JSON nodes file does not have the value.

Fix this by handling this nil value gracefully.

Relates to #9217 (closed)

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

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