Hotfix: fix-retrieval-of-default-subnet-cidr

Version Control Information

Source branch: hotfix/devel/fix-retrieval-of-default-subnet-cidr
Target branch: devel

Commits:

* Fixup !1049 from suggestions

In !1049 some additions were suggested but not applied. Among other things but
 most importantly this left a bug behind where the
 `get_default_value_in_tf_vars` function always returned `None`.
This commit cleans this up after the fact.

From: https://gitlab.com/yaook/k8s/-/merge_requests/1049#note_1885610407
Related: ebd723e5677d9794b29f94d98eb9b538bb5c6c02

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Merge Prerequisites

• MR title (and description) are descriptive
• Code is readable and syntactically correct
• Code is understandable
• Documentation has been updated, if necessary
• Commit messages look good
• Release note file in RST format added in latest commit

Superseeds: !1244 (closed)