Add a test.

Author: concretevitamin

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -289,7 +289,8 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] {
     } catch {
       case e: java.lang.IllegalArgumentException =>
         throw new TreeNodeException(
-          this, s"Failed to copy node.  Is otherCopyArgs specified correctly for $nodeName?")
+          this, s"Failed to copy node.  Is otherCopyArgs specified correctly for $nodeName? "
+            + s"Exception message: ${e.getMessage}.")
     }
   }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/trees/TreeNodeSuite.scala

@@ -22,6 +22,7 @@ import scala.collection.mutable.ArrayBuffer
 import org.scalatest.FunSuite
 
 import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.types.{StringType, NullType}
 
 class TreeNodeSuite extends FunSuite {
   test("top node changed") {
@@ -75,4 +76,29 @@ class TreeNodeSuite extends FunSuite {
 
     assert(expected === actual)
   }
+
+  test("transform works on nodes with Option children") {
+    case class Dummy(optKey: Option[Expression]) extends Expression {
+      def children = optKey.toSeq
+      def references = Set.empty[Attribute]
+      def nullable = true
+      def dataType = NullType
+      override lazy val resolved = true
+      type EvaluatedType = Any
+      def eval(input: Row) = null.asInstanceOf[Any]
+    }
+    val dummy1 = Dummy(Some(Literal("1", StringType)))
+    val dummy2 = Dummy(None)
+    val toZero: PartialFunction[Expression, Expression] =  { case Literal(_, _) => Literal(0) }
+
+    var actual = dummy1 transformDown toZero
+    assert(actual === Dummy(Some(Literal(0))))
+
+    actual = dummy1 transformUp toZero
+    assert(actual === Dummy(Some(Literal(0))))
+
+    actual = dummy2 transform toZero
+    assert(actual === Dummy(None))
+  }
+
 }