Github user rxin commented on the pull request:
https://github.com/apache/spark/pull/1428#issuecomment-49125623
I've already merged this. I think we should re-evaluate in the future
whether we should push some stuff into foldable itself, because as I see it a
lot of the pattern matching rules in NullPropagation could potentially be
implemented by each expression itself to be foldable. I think that might also
lead to higher planner performance (although that's probably less important).
More importantly, it does feel more natural to me that this stuff goes into
each expression, rather than having a rule for each NullPropagation.
cc @marmbrus
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