Add a test for the edge case where the value is an empty string, two-fer

[santi020k]

Although it's a very simple exercise, during a mentoring discussion, I found it interesting to consider the possibility of having this additional test, as it's a scenario that could happen in real life where a user might try to pass an empty string value. It's a very simple change; I just added an edge case to the two-fer tests. Feel free to reject this PR if you deem it necessary.

[github-actions]

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[SleeplessByte]

Thank you for the PR.

We're not going to complicate two-fer, but discussing things like this during mentoring sessions is excellent!