chore: change `getOffset()` to always return (never null)

[ghiscoding]

• prior to the code change, we could provide an undefined/null element which would have returned an undefined result, but I think it's better to always return and if the element is really null then we should check it before calling the method
• this code change is also simplifies the code a lot too

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.8%. Comparing base (da2df8f) to head (78a5e76).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1626 +/- ## ======================================== - Coverage 99.8% 99.8% -0.0% ======================================== Files 198 198 Lines 21805 21799 -6 Branches 7307 7002 -305 ======================================== - Hits 21744 21738 -6 - Misses 55 61 +6 + Partials 6 0 -6 ```

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