Only set `breaker` when stats are retrieved

When communicating with 1.3 and earlier nodes, it's possible that the
field data breaker info is not sent at all. When this happens, we should
leave the `breaker` variable as-is (unset) instead of creating an
AllCircuitBreakerStats object with a null fd breaker and fake request &
parent breakers.

src/main/java/org/elasticsearch/action/admin/cluster/node/stats/NodeStats.java

@@ -223,10 +223,12 @@ public class NodeStats extends NodeOperationResponse implements ToXContent {
         } else {
             // If 1.3.0 or earlier, only a single CircuitBreakerStats can be read
             CircuitBreakerStats fdStats = CircuitBreakerStats.readOptionalCircuitBreakerStats(in);
+            if (fdStats != null) {
                 CircuitBreakerStats reqStats = new CircuitBreakerStats(CircuitBreaker.Name.REQUEST, 0, 0, 1.0, -1);
                 CircuitBreakerStats parentStats = new CircuitBreakerStats(CircuitBreaker.Name.PARENT, 0, 0, 1.0, -1);
                 breaker = new AllCircuitBreakerStats(new CircuitBreakerStats[] {parentStats, fdStats, reqStats});
             }
+        }
 
     }
 

src/test/java/org/elasticsearch/bwcompat/NodesStatsBasicBackwardsCompat.java

@@ -0,0 +1,89 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.bwcompat;
+
+import org.elasticsearch.action.admin.cluster.node.info.NodeInfo;
+import org.elasticsearch.action.admin.cluster.node.info.NodesInfoResponse;
+import org.elasticsearch.action.admin.cluster.node.stats.NodesStatsRequestBuilder;
+import org.elasticsearch.action.admin.cluster.node.stats.NodesStatsResponse;
+import org.elasticsearch.client.transport.TransportClient;
+import org.elasticsearch.common.settings.ImmutableSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ElasticsearchBackwardsCompatIntegrationTest;
+import org.elasticsearch.test.ElasticsearchIntegrationTest;
+import org.junit.Test;
+
+import java.lang.reflect.Method;
+
+
+@ElasticsearchIntegrationTest.ClusterScope(scope= ElasticsearchIntegrationTest.Scope.SUITE,  numClientNodes = 0)
+public class NodesStatsBasicBackwardsCompat extends ElasticsearchBackwardsCompatIntegrationTest {
+
+    @Test
+    public void testNodeStatsSetIndices() throws Exception {
+        createIndex("test");
+
+        NodesInfoResponse nodesInfo = client().admin().cluster().prepareNodesInfo().execute().actionGet();
+
+        Settings settings = ImmutableSettings.settingsBuilder()
+                .put("client.transport.ignore_cluster_name", true).build();
+
+        // We explicitly connect to each node with a custom TransportClient
+        for (NodeInfo n : nodesInfo.getNodes()) {
+            TransportClient tc = new TransportClient(settings).addTransportAddress(n.getNode().address());
+
+            // Just verify that the NS can be sent and serialized/deserialized between nodes with basic indices
+            NodesStatsResponse ns = tc.admin().cluster().prepareNodesStats().setIndices(true).execute().actionGet();
+        }
+    }
+
+    @Test
+    public void testNodeStatsSetRandom() throws Exception {
+        createIndex("test");
+
+        NodesInfoResponse nodesInfo = client().admin().cluster().prepareNodesInfo().execute().actionGet();
+
+        Settings settings = ImmutableSettings.settingsBuilder()
+                .put("client.transport.ignore_cluster_name", true).build();
+
+        // We explicitly connect to each node with a custom TransportClient
+        for (NodeInfo n : nodesInfo.getNodes()) {
+            TransportClient tc = new TransportClient(settings).addTransportAddress(n.getNode().address());
+
+            // randomize the combination of flags set
+            // Uses reflection to find methods in an attempt to future-proof this test against newly added flags
+            NodesStatsRequestBuilder nsBuilder = tc.admin().cluster().prepareNodesStats();
+
+            Class c = nsBuilder.getClass();
+            for (Method method : c.getDeclaredMethods()) {
+                if (method.getName().startsWith("set")) {
+                    if (method.getParameterTypes().length == 1 && method.getParameterTypes()[0] == boolean.class) {
+                        method.invoke(nsBuilder, randomBoolean());
+                    }
+                } else if ((method.getName().equals("all") || method.getName().equals("clear")) && randomBoolean()) {
+                    method.invoke(nsBuilder);
+                }
+            }
+            NodesStatsResponse ns = nsBuilder.execute().actionGet();
+
+        }
+    }
+
+}