mutable.BitSet in ALS not serializable with KryoSerializer

Caused by: org.apache.spark.SparkException: Job aborted due to stage failure: Task 1724.0:9 failed 4 times, most recent failure: Exception failure in TID 68548 on host lon4-hadoopslave-b232.lon4.spotify.net: com.esotericsoftware.kryo.KryoException: java.lang.ArrayStoreException: scala.collection.mutable.HashSet
Serialization trace:
shouldSend (org.apache.spark.mllib.recommendation.OutLinkBlock)
        com.esotericsoftware.kryo.serializers.FieldSerializer$ObjectField.read(FieldSerializer.java:626)
        com.esotericsoftware.kryo.serializers.FieldSerializer.read(FieldSerializer.java:221)
        com.esotericsoftware.kryo.Kryo.readClassAndObject(Kryo.java:732)
        com.twitter.chill.Tuple2Serializer.read(TupleSerializers.scala:43)
        com.twitter.chill.Tuple2Serializer.read(TupleSerializers.scala:34)
        com.esotericsoftware.kryo.Kryo.readClassAndObject(Kryo.java:732)
        org.apache.spark.serializer.KryoDeserializationStream.readObject(KryoSerializer.scala:115)
        org.apache.spark.serializer.DeserializationStream$$anon$1.getNext(Serializer.scala:125)
        org.apache.spark.util.NextIterator.hasNext(NextIterator.scala:71)
        org.apache.spark.InterruptibleIterator.hasNext(InterruptibleIterator.scala:39)
        org.apache.spark.rdd.CoGroupedRDD$$anonfun$compute$4.apply(CoGroupedRDD.scala:155)
        org.apache.spark.rdd.CoGroupedRDD$$anonfun$compute$4.apply(CoGroupedRDD.scala:154)
        scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
        scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
        org.apache.spark.rdd.CoGroupedRDD.compute(CoGroupedRDD.scala:154)
        org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
        org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
        org.apache.spark.rdd.MappedValuesRDD.compute(MappedValuesRDD.scala:31)
        org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
        org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
        org.apache.spark.rdd.FlatMappedValuesRDD.compute(FlatMappedValuesRDD.scala:31)
        org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
        org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
        org.apache.spark.rdd.FlatMappedRDD.compute(FlatMappedRDD.scala:33)
        org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
        org.apache.spark.CacheManager.getOrCompute(CacheManager.scala:77)
        org.apache.spark.rdd.RDD.iterator(RDD.scala:227)
        org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:111)
        org.apache.spark.scheduler.Task.run(Task.scala:51)
        org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:187)
        java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        java.lang.Thread.run(Thread.java:662)
Driver stacktrace:
	at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1033)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1017)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1015)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1015)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:633)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:633)
	at scala.Option.foreach(Option.scala:236)
	at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:633)
	at org.apache.spark.scheduler.DAGSchedulerEventProcessActor$$anonfun$receive$2.applyOrElse(DAGScheduler.scala:1207)
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
	at akka.actor.ActorCell.invoke(ActorCell.scala:456)
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
	at akka.dispatch.Mailbox.run(Mailbox.scala:219)
	at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:386)
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)