Github user mateiz commented on a diff in the pull request: https://github.com/apache/spark/pull/1551#discussion_r15562646 --- Diff: core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala --- @@ -344,7 +345,12 @@ private[spark] object PythonRDD extends Logging { throw new SparkException("Unexpected Tuple2 element type " + pair._1.getClass) } case other => - throw new SparkException("Unexpected element type " + first.getClass) + if (other == null) { + dataOut.writeInt(SpecialLengths.NULL) + writeIteratorToStream(iter, dataOut) --- End diff -- But this is what I didn't understand about the whole PR: user code is not meant to call PythonRDD directly. Note that the whole PythonRDD object is `private[spark]`. So where in the codebase today can we get nulls there?
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