Fix possible NPE in ClusterState.toString()

ClusterState.toString() can throw NPE if at least on index template exists in the cluster state.

src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -297,7 +297,11 @@ public class ClusterState implements ToXContent {
                 builder.field("order", templateMetaData.order());
 
                 builder.startObject("settings");
-                Settings settings = settingsFilter.filterSettings(templateMetaData.settings());
+                Settings settings = templateMetaData.settings();
+                if (settingsFilter != null) {
+                    settings = settingsFilter.filterSettings(settings);
+                }
+
                 for (Map.Entry<String, String> entry : settings.getAsMap().entrySet()) {
                     builder.field(entry.getKey(), entry.getValue());
                 }
@@ -331,7 +335,7 @@ public class ClusterState implements ToXContent {
                 builder.startObject("settings");
                 Settings settings = indexMetaData.settings();
                 if (settingsFilter != null) {
-                    settings = settingsFilter.filterSettings(indexMetaData.settings());
+                    settings = settingsFilter.filterSettings(settings);
                 }
                 for (Map.Entry<String, String> entry : settings.getAsMap().entrySet()) {
                     builder.field(entry.getKey(), entry.getValue());

src/test/java/org/elasticsearch/cluster/serialization/ClusterStateToStringTests.java

@@ -0,0 +1,49 @@
+package org.elasticsearch.cluster.serialization;
+
+import org.elasticsearch.Version;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.cluster.metadata.IndexTemplateMetaData;
+import org.elasticsearch.cluster.metadata.MetaData;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.routing.RoutingTable;
+import org.elasticsearch.cluster.routing.allocation.AllocationService;
+import org.elasticsearch.common.transport.DummyTransportAddress;
+import org.elasticsearch.test.ElasticsearchTestCase;
+import org.junit.Test;
+
+import static org.hamcrest.Matchers.containsString;
+
+/**
+ *
+ */
+public class ClusterStateToStringTests extends ElasticsearchTestCase {
+    @Test
+    public void testClusterStateSerialization() throws Exception {
+        MetaData metaData = MetaData.builder()
+                .put(IndexMetaData.builder("test_idx").numberOfShards(10).numberOfReplicas(1))
+                .put(IndexTemplateMetaData.builder("test_template").build())
+                .build();
+
+        RoutingTable routingTable = RoutingTable.builder()
+                .addAsNew(metaData.index("test_idx"))
+                .build();
+
+        DiscoveryNodes nodes = DiscoveryNodes.builder().put(new DiscoveryNode("node_foo", DummyTransportAddress.INSTANCE, Version.CURRENT)).localNodeId("node_foo").masterNodeId("node_foo").build();
+
+        ClusterState clusterState = ClusterState.builder().nodes(nodes).metaData(metaData).routingTable(routingTable).build();
+
+        AllocationService strategy = new AllocationService();
+        clusterState = ClusterState.builder(clusterState).routingTable(strategy.reroute(clusterState).routingTable()).build();
+
+        String clusterStateString = clusterState.toString();
+        assertNotNull(clusterStateString);
+
+        assertThat(clusterStateString, containsString("test_idx"));
+        assertThat(clusterStateString, containsString("test_template"));
+        assertThat(clusterStateString, containsString("node_foo"));
+
+    }
+
+}