The node reports an error during the recovery process

[medivn]

elasticsearch version:6.2.4
The node reports an error during the recovery process. From the code point of view, it is because there is no judgment whether the string is empty, but why does the Translog have such abnormal data that causes the error?
The log is as follows

[2019-06-14T13:54:10,636][WARN ][o.e.i.c.IndicesClusterStateService] [node-2] [[indexName][1]] marking and sending shard failed due to [failed recovery]
org.elasticsearch.indices.recovery.RecoveryFailedException: [indexName][1]: Recovery failed from {node-1}{NYI9biLCQ2W3uJ3mOu5W3A}{bu-VpLxTQvO1AvYwmTNc4g}{192.168.60.78}{192.168.60.78:9300}{ml.machine_memory=16726286336, ml.max_open_jobs=20, ml.enabled=true} into {node-2}{PCcLeyjkREeZ08kEuR0GdQ}{bSKzgm0iRIKLHEgVTeXuMA}{192.168.60.94}{192.168.60.94:9300}{ml.machine_memory=16726286336, ml.max_open_jobs=20, ml.enabled=true}
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService.doRecovery(PeerRecoveryTargetService.java:288) [elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService.access$900(PeerRecoveryTargetService.java:81) [elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService$RecoveryRunner.doRun(PeerRecoveryTargetService.java:635) [elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:672) [elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-6.2.4.jar:6.2.4]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_161]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_161]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]
Caused by: org.elasticsearch.transport.RemoteTransportException: [node-1][192.168.60.78:9300][internal:index/shard/recovery/start_recovery]
Caused by: org.elasticsearch.index.engine.RecoveryEngineException: Phase[2] phase2 failed
	at org.elasticsearch.indices.recovery.RecoverySourceHandler.recoverToTarget(RecoverySourceHandler.java:211) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoverySourceService.recover(PeerRecoverySourceService.java:98) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoverySourceService.access$000(PeerRecoverySourceService.java:50) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoverySourceService$StartRecoveryTransportRequestHandler.messageReceived(PeerRecoverySourceService.java:107) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoverySourceService$StartRecoveryTransportRequestHandler.messageReceived(PeerRecoverySourceService.java:104) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TransportRequestHandler.messageReceived(TransportRequestHandler.java:30) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:66) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TcpTransport$RequestHandler.doRun(TcpTransport.java:1555) ~[elasticsearch-6.2.4.jar:6.2.4]
	... 5 more
Caused by: org.elasticsearch.transport.RemoteTransportException: [node-2][192.168.60.94:9300][internal:index/shard/recovery/translog_ops]
Caused by: org.elasticsearch.index.translog.TranslogException: Failed to write operation [NoOp{seqNo=452743, primaryTerm=18, reason='null'}]
	at org.elasticsearch.index.translog.Translog.add(Translog.java:500) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.engine.InternalEngine.index(InternalEngine.java:890) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.index(IndexShard.java:738) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.applyIndexOperation(IndexShard.java:707) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.applyTranslogOperation(IndexShard.java:1245) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.RecoveryTarget.indexTranslogOperations(RecoveryTarget.java:403) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService$TranslogOperationsRequestHandler.messageReceived(PeerRecoveryTargetService.java:460) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService$TranslogOperationsRequestHandler.messageReceived(PeerRecoveryTargetService.java:451) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TransportRequestHandler.messageReceived(TransportRequestHandler.java:30) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:66) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TcpTransport$RequestHandler.doRun(TcpTransport.java:1555) ~[elasticsearch-6.2.4.jar:6.2.4]
	... 5 more
Caused by: java.lang.NullPointerException
	at org.elasticsearch.common.io.stream.StreamOutput.writeString(StreamOutput.java:320) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.translog.Translog$NoOp.write(Translog.java:1333) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.translog.Translog$NoOp.access$500(Translog.java:1295) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.translog.Translog$Operation.writeOperation(Translog.java:908) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.translog.Translog.writeOperationNoSize(Translog.java:1475) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.translog.Translog.add(Translog.java:476) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.engine.InternalEngine.index(InternalEngine.java:890) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.index(IndexShard.java:738) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.applyIndexOperation(IndexShard.java:707) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.index.shard.IndexShard.applyTranslogOperation(IndexShard.java:1245) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.RecoveryTarget.indexTranslogOperations(RecoveryTarget.java:403) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService$TranslogOperationsRequestHandler.messageReceived(PeerRecoveryTargetService.java:460) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.indices.recovery.PeerRecoveryTargetService$TranslogOperationsRequestHandler.messageReceived(PeerRecoveryTargetService.java:451) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TransportRequestHandler.messageReceived(TransportRequestHandler.java:30) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:66) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.transport.TcpTransport$RequestHandler.doRun(TcpTransport.java:1555) ~[elasticsearch-6.2.4.jar:6.2.4]
	... 5 more

[elasticmachine]

Pinging @elastic/es-distributed

[ywelsch]

The NullPointerException is a bug that was fixed in later versions (#33141). Please upgrade.

[dnhatn]

@medivn Thank you for reporting this issue. Closing as this was fixed in #33141.