NoSuchElementException when restarting spark-notebook after failure

[markpavey]

If I have a notebook open with a running kernel and then kill the spark-notebook process and try to restart it I get the following output:

2017-12-06 16:34:10 WARN application:111 - Logger configuration in conf files is deprecated and has no effect. Use a logback configuration file instead.
2017-12-06 16:34:11 INFO Slf4jLogger:92 - Slf4jLogger started
2017-12-06 16:34:11 WARN application:111 - application.langs is deprecated, use play.i18n.langs instead
2017-12-06 16:34:11 WARN application:111 - conf\application.conf: 8: application.secret is deprecated, use play.crypto.secret instead
2017-12-06 16:34:11 INFO Play:92 - Application started (Prod)
2017-12-06 16:34:11 INFO NettyServer:92 - Listening for HTTP on /0:0:0:0:0:0:0:0:9000
[DEBUG] [12/06/2017 16:34:12.113] [netty-event-loop-3] [EventStream] StandardOutLogger started
2017-12-06 16:34:12 INFO Slf4jLogger:92 - Slf4jLogger started
[DEBUG] [12/06/2017 16:34:12.143] [netty-event-loop-3] [EventStream(akka://NotebookServer)] logger log1-Slf4jLogger started
[DEBUG] [12/06/2017 16:34:12.145] [netty-event-loop-3] [EventStream(akka://NotebookServer)] Default Loggers started
2017-12-06 16:34:12 INFO Remoting:107 - Starting remoting
2017-12-06 16:34:12 INFO Remoting:107 - Remoting started; listening on addresses :[akka.tcp://NotebookServer@127.0.0.1:14427]
2017-12-06 16:34:12 INFO Remoting:107 - Remoting now listens on addresses: [akka.tcp://NotebookServer@127.0.0.1:14427]
2017-12-06 16:34:12 INFO application:92 - io.provider_timeout: 89000 ms
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.initial_commit
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.save
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.remove
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.move
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.initial_commit
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.save
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.remove
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: messages.move
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: branch
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: authentication.key_file
2017-12-06 16:34:12 WARN ConfigurationMissingException:42 - ConfigurationMissingException: key missing: authentication.key_file_passphrase
2017-12-06 16:34:12 INFO application:92 - Notebooks dir is C:\test\spark-notebook\repo
2017-12-06 16:34:12 INFO application:92 - Notebook directory is: C:\test\spark-notebook\repo
2017-12-06 16:34:13 ERROR WebSocketFlowHandler:140 - WebSocket flow threw exception
java.util.NoSuchElementException
at scala.collection.concurrent.TrieMap.apply(TrieMap.scala:837)
at controllers.Application$$anonfun$openKernel$1.apply(Application.scala:506)
at controllers.Application$$anonfun$openKernel$1.apply(Application.scala:506)
at controllers.Application$ImperativeWebsocket$$anonfun$69.apply(Application.scala:809)
at controllers.Application$ImperativeWebsocket$$anonfun$69.apply(Application.scala:808)
at play.api.libs.iteratee.Concurrent$$anon$10$$anonfun$apply$3.apply$mcV$sp(Concurrent.scala:514)
at play.api.libs.iteratee.Concurrent$$anon$10$$anonfun$apply$3.apply(Concurrent.scala:514)
at play.api.libs.iteratee.Concurrent$$anon$10$$anonfun$apply$3.apply(Concurrent.scala:514)
at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:39)
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:415)
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
2017-12-06 16:34:16 ERROR WebSocketFlowHandler:140 - WebSocket flow threw exception

The NoSuchElementException then repeats every couple of seconds.

It looks like a similar cause to Issue #880 so I presume a similar fix would work?