[ML] NPE thrown ocasionally when trying to open an anomaly detection job

[dolaru]

Spotted in 8.0.0, single node.

Sometimes, when trying to open a anomaly detection job, the HTTP response says:

{
  "reason" : null,
  "type" : "null_pointer_exception",
  "root_cause" : [ {
    "reason" : null,
    "type" : "null_pointer_exception"
  } ]
}

ES Logs:

[2019-11-15T00:08:16,094][DEBUG][o.e.a.s.m.TransportMasterNodeAction] [ML-QA-WINDOWS-4] unexpected exception during publication
java.lang.NullPointerException: null
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.calculateCurrentLoadForNode(JobNodeSelector.java:272) ~[?:?]
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.selectNode(JobNodeSelector.java:114) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.getAssignment(TransportOpenJobAction.java:411) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:422) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:340) ~[?:?]
    at org.elasticsearch.persistent.PersistentTasksClusterService$1.execute(PersistentTasksClusterService.java:105) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.ClusterStateUpdateTask.execute(ClusterStateUpdateTask.java:47) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.executeTasks(MasterService.java:697) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.calculateTaskOutputs(MasterService.java:319) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.runTasks(MasterService.java:214) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService$Batcher.run(MasterService.java:151) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher.runIfNotProcessed(TaskBatcher.java:150) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher$BatchedTask.run(TaskBatcher.java:188) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:699) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:252) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:215) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
    at java.lang.Thread.run(Thread.java:830) [?:?]
[2019-11-15T00:08:16,096][DEBUG][o.e.a.s.m.TransportMasterNodeAction] [ML-QA-WINDOWS-4] unexpected exception during publication
java.lang.NullPointerException: null
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.calculateCurrentLoadForNode(JobNodeSelector.java:272) ~[?:?]
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.selectNode(JobNodeSelector.java:114) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.getAssignment(TransportOpenJobAction.java:411) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:422) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:340) ~[?:?]
    at org.elasticsearch.persistent.PersistentTasksClusterService$1.execute(PersistentTasksClusterService.java:105) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.ClusterStateUpdateTask.execute(ClusterStateUpdateTask.java:47) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.executeTasks(MasterService.java:697) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.calculateTaskOutputs(MasterService.java:319) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.runTasks(MasterService.java:214) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService$Batcher.run(MasterService.java:151) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher.runIfNotProcessed(TaskBatcher.java:150) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher$BatchedTask.run(TaskBatcher.java:188) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:699) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:252) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:215) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
    at java.lang.Thread.run(Thread.java:830) [?:?]
[2019-11-15T00:08:16,097][WARN ][r.suppressed             ] [ML-QA-WINDOWS-4] path: /_ml/anomaly_detectors/some_job_1573776495_800_6085/_open, params: {job_id=some_job_1573776495_800_6085}
java.lang.NullPointerException: null
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.calculateCurrentLoadForNode(JobNodeSelector.java:272) ~[?:?]
    at org.elasticsearch.xpack.ml.job.JobNodeSelector.selectNode(JobNodeSelector.java:114) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.getAssignment(TransportOpenJobAction.java:411) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:422) ~[?:?]
    at org.elasticsearch.xpack.ml.action.TransportOpenJobAction$OpenJobPersistentTasksExecutor.validate(TransportOpenJobAction.java:340) ~[?:?]
    at org.elasticsearch.persistent.PersistentTasksClusterService$1.execute(PersistentTasksClusterService.java:105) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.ClusterStateUpdateTask.execute(ClusterStateUpdateTask.java:47) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.executeTasks(MasterService.java:697) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.calculateTaskOutputs(MasterService.java:319) ~[elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService.runTasks(MasterService.java:214) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.MasterService$Batcher.run(MasterService.java:151) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher.runIfNotProcessed(TaskBatcher.java:150) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.cluster.service.TaskBatcher$BatchedTask.run(TaskBatcher.java:188) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:699) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:252) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:215) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
    at java.lang.Thread.run(Thread.java:830) [?:?]

[elasticmachine]

Pinging @elastic/ml-core (:ml)