KryoSerializer return null when deserialize Task obj in Executor

[林武康]

Hi all, I changed spark.closure.serializer to kryo, when I try count action in 
spark shell the Task obj deserialize in Executor return null, src line is: 
override def run(){
......
task = ser.deserializer[Task[Any]](...)
......
}
Where task is null
Can any one help me? Thank you!