Following the null handling semantics of the Max and Min methods, the new MaxBy and MinBy methods have been designed to skip any elements yielding null keys. As a side-effect of the behavior, the methods will return the last element in a sequence if every key turns out to be null. While this does not produce any observable difference in the Max and Min methods, it does do so in the MaxBy and MinBy case. In fact it is inconsistent with how the same methods treat sequences returning identical non-null keys, where the first element is always favored.

I do not believe this to be a breaking change, since our documentation provides no guarantee on what element will get returned in the event of a tie.

Fixes #61317.