[SPARK-2052] [SQL] Add optimization for CaseConversionExpression's.

Add optimization for `CaseConversionExpression`'s.
Yes please.
On Jun 9, 2014 8:16 PM, "Takuya UESHIN" <notifications@github.com> wrote:

> In
> sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
>
> > @@ -154,6 +155,10 @@ object NullPropagation extends Rule[LogicalPlan] {
> >          case left :: Literal(null, _) :: Nil => Literal(null, e.dataType)
> >          case _ => e
> >        }
> > +      case e: CaseConversionExpression => e.children match {
>
> Fixed the two points.
> Should I remove the mentioned lines?
>
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> <https://github.com/apache/spark/pull/990/files#r13576056>.
>