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/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportStartTransformAction.java
listener.onFailure(
                        new ElasticsearchStatusException(
                            TransformMessages.getMessage(CANNOT_START_FAILED_TRANSFORM, request.getId(), transformState.getReason()),
                            RestStatus.CONFLICT
                        )
                    );
                } else {
                    
                    
                    listener.onFailure(
                        new ElasticsearchStatusException(
                            "Cannot start transform [{}] as it is already started.",
                            RestStatus.CONFLICT,
                            request.getId()
                        )
                    );
                }
            }
        }, listener::onFailure);
        
        ActionListener<ValidateTransformAction.Response> validationListener = ActionListener.wrap(validationResponse -> {
            if (Boolean.TRUE.equals(transformConfigHolder.get().getSettings().getUnattended())) {
                logger.debug(
                    () -> format("[%s] Skip dest index creation as this is an unattended transform", transformConfigHolder.get().getId())
                );
                createOrGetIndexListener.onResponse(true);
                return;
            }
            TransformIndex.createDestinationIndex(
                client,