我实现了一个processfunction，它使用guava缓存过滤传入事件流。代码如下所示：

object myJob {
 private def updateCache(cacheObject, someValue) = {}
 private def getCacheValue(cacheObject, someKey) = {}

 override def run(params, executionEnv) = {
  val inputStream = executionEnv.stream

  val c = CacheBuilder.newBuilder()

  val outStream = inputStream.process(new ProcessFunction() { 
    updateCache()
    getCacheValue} 
    )
 }
}

向flink提交作业时，出现以下错误：

Caused by: org.apache.flink.api.common.InvalidProgramException: The implementation of the ProcessFunction is not serializable. The object probably contains or references non serializable fields.
at org.apache.flink.api.java.ClosureCleaner.clean(ClosureCleaner.java:99)
at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.clean(StreamExecutionEnvironment.java:1560)
at org.apache.flink.streaming.api.datastream.DataStream.clean(DataStream.java:185)
at org.apache.flink.streaming.api.datastream.DataStream.process(DataStream.java:666)
at org.apache.flink.streaming.api.scala.DataStream.process(DataStream.scala:686)

知道我做错了什么吗？如何解决此序列化错误？