Fixed the rule.

Author: rxin

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala

@@ -220,19 +220,21 @@ object HiveTypeCoercion {
         // Skip nodes who's children have not been resolved yet.
         case e if !e.childrenResolved => e
 
+        case b @ BinaryOperator(left, right)
+          if left.dataType == NullType &&  right.dataType == NullType =>
+          // If both inputs are null type (from null literals), cast the null type into some
+          // specific type the expression expects, so expressions don't need to handle NullType
+          val newLeft = Cast(left, b.inputType.defaultConcreteType)
+          val newRight = Cast(right, b.inputType.defaultConcreteType)
+          b.makeCopy(Array(newLeft, newRight))
+
         case b @ BinaryOperator(left, right) if left.dataType != right.dataType =>
           findTightestCommonTypeOfTwo(left.dataType, right.dataType).map { commonType =>
             if (b.inputType.acceptsType(commonType)) {
               // If the expression accepts the tighest common type, cast to that.
               val newLeft = if (left.dataType == commonType) left else Cast(left, commonType)
               val newRight = if (right.dataType == commonType) right else Cast(right, commonType)
               b.makeCopy(Array(newLeft, newRight))
-            } else if (commonType == NullType) {
-              // If the common type is null type (from null literals), cast the null type into the
-              // first accepted type.
-              val newLeft = Cast(left, b.inputType.defaultConcreteType)
-              val newRight = Cast(right, b.inputType.defaultConcreteType)
-              b.makeCopy(Array(newLeft, newRight))
             } else {
               // Otherwise, don't do anything with the expression.
               b

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercionSuite.scala

@@ -197,7 +197,9 @@ class HiveTypeCoercionSuite extends PlanTest {
   test("null literals handling for binary operators") {
     ruleTest(HiveTypeCoercion.WidenTypes,
       Add(Literal.create(null, NullType), Literal.create(null, NullType)),
-      Add(Literal.create(null, DoubleType), Literal.create(null, DoubleType)))
+      Add(
+        Cast(Literal.create(null, NullType), DoubleType),
+        Cast(Literal.create(null, NullType), DoubleType)))
   }
 
   test("coalesce casts") {