Improve test assertion

[jvz]

This fixes a test to check an empty map using a proper method rather than relying on its toString representation.

No JIRA nor changelog entry, trivial improvement.

Proposed changelog entries

Submitter checklist

- [ ] JIRA issue is well described
- [ ] Changelog entry appropriate for the audience affected by the change (users or developer, depending on the change). Examples
* Use the Internal: prefix if the change has no user-visible impact (API, test frameworks, etc.)
- [ ] Appropriate autotests or explanation to why this change has no tests
- [ ] For dependency updates: links to external changelogs and, if possible, full diffs

Desired reviewers

@reviewbybees

[Wadeck]

Code is good
Please adjust the description of the PR by removing the non applicable sections instead of letting the default text (removing everything between See [...] full diffs)

[batmat]

FTR, two tests are failing, and unrelated. Known issue that is being fixed in #3795.

👍 @jvz also as Wadeck said, please complete all fields required in the PR template. I agree here no changelog entry at all is perfect.
Also I recommend to either check a checkbox, or cross the whole item (given generally items are not optional, and showing you saw it but that's it's N/A is better for accelerating reviews)

[batmat]

Did it myself this time to shorten the cycle. But remember it next time :-).

[batmat]

This looks ready.
I think I will merge this later today, if nobody objects or does this before I do.

Thanks Matt!