Fix tupleElement to return Null for Null argument

Why it matters

This fix addresses an inconsistency in the tupleElement function where it did not return Null if its argument was Null. Ensuring that the function returns Null properly improves correctness and predictability when working with nullable data in tuples.

How to use it

Users do not need to change their queries. The fixed behavior of tupleElement returning Null on Null arguments is applied automatically after upgrading to the version containing this fix.