Flink ValueState<Long>配置了TTL，CheckPoint报空指针

Flink CheckPoint时，配置TTL的ValueState 状态报NullPointException。

20:11:11,729 INFO  org.apache.flink.runtime.checkpoint.CheckpointCoordinator     - Decline checkpoint 13 by task d7aa78e851dd620b3e3742d2dd40e451 of job b5ee7a9090f8dbb19fe3e41eb63396ec at 82cef248-450b-4af2-b632-af6552becb44 @ 127.0.0.1 (dataPort=-1).
20:11:11,730 INFO  org.apache.flink.runtime.checkpoint.CheckpointCoordinator     - Discarding checkpoint 13 of job b5ee7a9090f8dbb19fe3e41eb63396ec.
java.lang.Exception: Could not materialize checkpoint 13 for operator Flat Map -> Sink: console-sink (1/1).
	at org.apache.flink.streaming.runtime.tasks.StreamTask$AsyncCheckpointRunnable.handleExecutionException(StreamTask.java:1100)
	at org.apache.flink.streaming.runtime.tasks.StreamTask$AsyncCheckpointRunnable.run(StreamTask.java:1042)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at org.apache.flink.runtime.concurrent.FutureUtils.runIfNotDoneAndGet(FutureUtils.java:450)
	at org.apache.flink.streaming.api.operators.OperatorSnapshotFinalizer.<init>(OperatorSnapshotFinalizer.java:47)
	at org.apache.flink.streaming.runtime.tasks.StreamTask$AsyncCheckpointRunnable.run(StreamTask.java:1011)
	... 3 more
Caused by: java.lang.NullPointerException
	at org.apache.flink.api.common.typeutils.base.LongSerializer.serialize(LongSerializer.java:69)
	at org.apache.flink.api.common.typeutils.base.LongSerializer.serialize(LongSerializer.java:32)
	at org.apache.flink.api.common.typeutils.CompositeSerializer.serialize(CompositeSerializer.java:142)
	at org.apache.flink.runtime.state.heap.CopyOnWriteStateMapSnapshot.writeState(CopyOnWriteStateMapSnapshot.java:116)
	at org.apache.flink.runtime.state.heap.AbstractStateTableSnapshot.writeStateInKeyGroup(AbstractStateTableSnapshot.java:121)
	at org.apache.flink.runtime.state.heap.CopyOnWriteStateTableSnapshot.writeStateInKeyGroup(CopyOnWriteStateTableSnapshot.java:37)
	at org.apache.flink.runtime.state.heap.HeapSnapshotStrategy$1.callInternal(HeapSnapshotStrategy.java:191)
	at org.apache.flink.runtime.state.heap.HeapSnapshotStrategy$1.callInternal(HeapSnapshotStrategy.java:158)
	at org.apache.flink.runtime.state.AsyncSnapshotCallable.call(AsyncSnapshotCallable.java:75)
	at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266)
	at java.util.concurrent.FutureTask.run(FutureTask.java)
	at org.apache.flink.runtime.concurrent.FutureUtils.runIfNotDoneAndGet(FutureUtils.java:447)
	... 5 more