I'm seeing quite a few of these in prod:

```
java.lang.NullPointerException: Cannot invoke "org.elasticsearch.xpack.core.transform.transforms.TransformState.getTaskState()" because "transformState" is null
    at org.elasticsearch.xpack.transform.TransformUsageTransportAction.masterOperation(TransformUsageTransportAction.java:106) ~[?:?]
    at org.elasticsearch.xpack.transform.TransformUsageTransportAction.masterOperation(TransformUsageTransportAction.java:55) ~[?:?]
    at org.elasticsearch.action.support.master.TransportMasterNodeAction.executeMasterOperation(TransportMasterNodeAction.java:124) ~[elasticsearch-8.9.0.jar:?]
    at org.elasticsearch.action.support.master.TransportMasterNodeAction$AsyncSingleAction.lambda$doStart$3(TransportMasterNodeAction.java:235) ~[elasticsearch-8.9.0.jar:?]
    at org.elasticsearch.action.ActionRunnable$3.doRun(ActionRunnable.java:72) ~[elasticsearch-8.9.0.jar:?]
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:983) ~[elasticsearch-8.9.0.jar:?]
    at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:26) ~[elasticsearch-8.9.0.jar:?]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144) ~[?:?]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642) ~[?:?]
    at java.lang.Thread.run(Thread.java:1623) ~[?:?]
```

`org.elasticsearch.persistent.PersistentTasksCustomMetadata.PersistentTask#getState` is declared `@Nullable` but this case is not handled properly by the usage action.
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportGetDataFrameAnalyticsStatsAction.java
AnalysisStats analysisStats
    ) {
        ClusterState clusterState = clusterService.state();
        PersistentTasksCustomMetadata tasks = clusterState.getMetadata().custom(PersistentTasksCustomMetadata.TYPE);
        PersistentTasksCustomMetadata.PersistentTask<?> analyticsTask = MlTasks.getDataFrameAnalyticsTask(concreteAnalyticsId, tasks);
        DataFrameAnalyticsState analyticsState = MlTasks.getDataFrameAnalyticsState(concreteAnalyticsId, tasks);
        String failureReason = null;
        if (analyticsState == DataFrameAnalyticsState.FAILED) {
            DataFrameAnalyticsTaskState taskState = (DataFrameAnalyticsTaskState) analyticsTask.getState();
            failureReason = taskState.getReason();
        }
        DiscoveryNode node = null;
        String assignmentExplanation = null;
        if (analyticsTask != null) {
            node = analyticsTask.getExecutorNode() != null ? clusterState.nodes().get(analyticsTask.getExecutorNode()) : null;
            assignmentExplanation = analyticsTask.getAssignment().getExplanation();
        }
        return new GetDataFrameAnalyticsStatsAction.Response.Stats(
            concreteAnalyticsId,
            analyticsState,
            failureReason,
            progress,
            dataCounts,
            memoryUsage,
            analysisStats,
            node,
            assignmentExplanation
        );
    }
    private static class RetrievedStatsHolder {