Convert `Option<Vec<sort expression>>` to `Vec<sort expression>`

[findepi]

Consider AggregateFunction.order_by field -- it is Option<Vec< /*sort expr*/ >> None means "no sorting" but this can be modeled as Some( vec![] ). Empty collection perfectly describes lack of sorting, so no need to wrap if with optional value.

Remove Option and keep just Vec.

This can be applied to

• AggregateFunction.order_by
• ExprFuncBuilder.order_by
• ...

based on https://github.com/apache/datafusion/pull/12178#discussion_r1732636238 cc @crepererum

[findepi]

take

[findepi]

plan to work on this after https://github.com/apache/datafusion/issues/12193, as the two will conflict.

[ViggoC]

Hi @findepi, can I take it if you do not work on it anymore?

[findepi]

sure, go for it!