Bugfix/correct mapper error

[davidporter-id-au]

What changed?
Fixes (hopefully) some mapping bugs I introduced with #6523 due to the version history being passed in being nil sometimes, therefore causing panics.

The mapping code as it's currently written panics (and is changed by this PR) which I think is the correct architectural choice. The mappers, by panicing as they presently are, are confusing validation with mapping. This corrects the mapper to gracefully handle nil input, and a quick survey appears to show that there are no expected areas which should never be nil that don't already have nil-check validation in place.

Why?

How did you test it?

• Unit tests
• Staging deploy

How did you test it?

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.39%. Comparing base (eacb093) to head (f4131dd).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
common/persistence/versionHistory.go	71.42%	2 Missing ⚠️

Files with missing lines	Coverage Δ
common/persistence/versionHistory.go	76.16% <71.42%> (+0.75%)	⬆️

... and 4 files with indirect coverage changes

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