Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/8881#discussion_r40509300
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/dstream/TransformedDStream.scala
---
@@ -38,6 +39,12 @@ class TransformedDStream[U: ClassTag] (
override def compute(validTime: Time): Option[RDD[U]] = {
val parentRDDs = parents.map(_.getOrCompute(validTime).orNull).toSeq
- Some(transformFunc(parentRDDs, validTime))
+ val transformedRDD = transformFunc(parentRDDs, validTime)
+ if (transformedRDD == null) {
--- End diff --
I don't have a strong opinion on this, but this could be done with
`require`. Generates a different exception -- `IllegalArgumentException`, but a
lower-level generic exception seems pretty reasonable.
Can I suggest tightening the text to something like "Transform function may
not return null. Return RDD.empty to return no elements as the result of the
transformation."
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