fix NPE in TransportGetDeploymentStatsAction (elastic#131678)

* fix NPE in TransportGetDeploymentStatsAction

* better fix

Author: jan-elastic

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportGetDeploymentStatsAction.java

@@ -261,13 +261,15 @@ static GetDeploymentStatsAction.Response addFailedRoutes(
                 List<AssignmentStats.NodeStats> nodeStats = new ArrayList<>();
 
                 for (var routingEntry : nonStartedEntries.getValue().entrySet()) {
-                    nodeStats.add(
-                        AssignmentStats.NodeStats.forNotStartedState(
-                            nodes.get(routingEntry.getKey()),
-                            routingEntry.getValue().getState(),
-                            routingEntry.getValue().getReason()
-                        )
-                    );
+                    if (nodes.nodeExists(routingEntry.getKey())) {
+                        nodeStats.add(
+                            AssignmentStats.NodeStats.forNotStartedState(
+                                nodes.get(routingEntry.getKey()),
+                                routingEntry.getValue().getState(),
+                                routingEntry.getValue().getReason()
+                            )
+                        );
+                    }
                 }
 
                 nodeStats.sort(Comparator.comparing(n -> n.getNode().getId()));