fix: exception with union of nullable types

[baywet]

fixes #5276

[calebkiage]

is this testable?

[baywet]

is this testable?

The author of the issue shared detailed repro. I was running out of time. But you could add a unit test from those if you don't mind please?
(Monday is a public holiday in Canada)

[baywet]

@calebkiage it took me a while to come back to this one, but finally got around to adding a unit test. Good for review.

[sonarqubecloud]

Quality Gate failed

Failed conditions
73.7% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud