Run tests / chore: Enable nullable for job/characteristics relating code (#2900) * chore: enable nullable for job/characteristics relating code * chore: fix nullable annotation of AssertHasValue * chore: add additional nullable annotations

Run tests / chore: Enable nullable for job/characteristics relating code (#2900) * chore: enable nullable for job/characteristics relating code * chore: fix nullable annotation of AssertHasValue * chore: add additional nullable annotations #1977