[SPARK-2093] [SQL] NullPropagation should use exact type value.

`NullPropagation` should use exact type value when transform `Count` or `Sum`.

Author: Takuya UESHIN <[email protected]>

Closes #1034 from ueshin/issues/SPARK-2093 and squashes the following commits:

65b6ff1 [Takuya UESHIN] Modify the literal value of the result of transformation from Sum to long value.
830c20b [Takuya UESHIN] Add Cast to the result of transformation from Count.
9314806 [Takuya UESHIN] Fix NullPropagation to use exact type value.

Author: ueshin

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -104,8 +104,8 @@ object ColumnPruning extends Rule[LogicalPlan] {
 object NullPropagation extends Rule[LogicalPlan] {
   def apply(plan: LogicalPlan): LogicalPlan = plan transform {
     case q: LogicalPlan => q transformExpressionsUp {
-      case e @ Count(Literal(null, _)) => Literal(0, e.dataType)
-      case e @ Sum(Literal(c, _)) if c == 0 => Literal(0, e.dataType)
+      case e @ Count(Literal(null, _)) => Cast(Literal(0L), e.dataType)
+      case e @ Sum(Literal(c, _)) if c == 0 => Cast(Literal(0L), e.dataType)
       case e @ Average(Literal(c, _)) if c == 0 => Literal(0.0, e.dataType)
       case e @ IsNull(c) if c.nullable == false => Literal(false, BooleanType)
       case e @ IsNotNull(c) if c.nullable == false => Literal(true, BooleanType)