fixed the NPE caused by closures being cleaned before being passed into the aggregate function

Author: dorx

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

@@ -1195,7 +1195,7 @@ abstract class RDD[T: ClassTag](
 
   /** User code that created this RDD (e.g. `textFile`, `parallelize`). */
   @transient private[spark] val creationSiteInfo = Utils.getCallSiteInfo
-  private[spark] def getCreationSite: String = creationSiteInfo.toString
+  private[spark] def getCreationSite: String = Option(creationSiteInfo).getOrElse("").toString
 
   private[spark] def elementClassTag: ClassTag[T] = classTag[T]