Fix NPE

Author: Andrew Or

core/src/main/scala/org/apache/spark/rdd/RDDOperationScope.scala

@@ -43,7 +43,7 @@ import org.apache.spark.SparkContext
 @JsonPropertyOrder(Array("id", "name", "parent"))
 private[spark] class RDDOperationScope(
     val name: String,
-    val parent: Option[RDDOperationScope] = None) {
+    val parent: Option[RDDOperationScope] = None) extends Serializable {
 
   val id: Int = RDDOperationScope.nextScopeId()
 

streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala

@@ -117,7 +117,7 @@ abstract class DStream[T: ClassTag] (
    * Instead, every time we call `compute` we instantiate a new scope using the same name as this
    * one. Otherwise, all RDDs ever created by this DStream will be in the same scope.
    */
-  @transient private val scope: Option[RDDOperationScope] = {
+  private val scope: Option[RDDOperationScope] = {
     Option(ssc.sc.getLocalProperty(SparkContext.RDD_SCOPE_KEY)).map(RDDOperationScope.fromJson)
   }