Fix NPE in IntermedaiteStateCalcStage

helix-core/src/main/java/org/apache/helix/controller/stages/IntermediateStateCalcStage.java

@@ -864,7 +864,7 @@ private void computeIntermediateMap(PartitionStateMap intermediateStateMap,
       entry.getValue().forEach((key, value) -> {
         if (!value.getToState().equals(HelixDefinedState.DROPPED.name())) {
           intermediateStateMap.setState(entry.getKey(), value.getTgtName(), value.getToState());
-        } else {
+        } else if (intermediateStateMap.getStateMap().containsKey(entry.getKey())) {
           intermediateStateMap.getStateMap().get(entry.getKey()).remove(value.getTgtName());
         }
       });

helix-core/src/test/java/org/apache/helix/controller/stages/TestIntermediateStateCalcStage.java

@@ -572,6 +572,84 @@ public void testPartitionMissing() {
     }
   }
 
+  @Test
+  public void testMessageAlreadyApplied() {
+    String resourcePrefix = "resource";
+    int nResource = 1;
+    int nPartition = 5;
+    int nReplica = 1;
+
+    String[] resources = new String[nResource];
+    for (int i = 0; i < nResource; i++) {
+      resources[i] = resourcePrefix + "_" + i;
+    }
+
+    preSetup(resources, nReplica, nReplica);
+    event.addAttribute(AttributeName.RESOURCES.name(), getResourceMap(resources, nPartition, "OnlineOffline"));
+    event.addAttribute(AttributeName.RESOURCES_TO_REBALANCE.name(),
+        getResourceMap(resources, nPartition, "OnlineOffline"));
+
+    // Initialize bestpossible state and current state
+    BestPossibleStateOutput bestPossibleStateOutput = new BestPossibleStateOutput();
+    CurrentStateOutput currentStateOutput = new CurrentStateOutput();
+    MessageOutput messageSelectOutput = new MessageOutput();
+    IntermediateStateOutput expectedResult = new IntermediateStateOutput();
+
+    _clusterConfig.setErrorOrRecoveryPartitionThresholdForLoadBalance(1);
+    setClusterConfig(_clusterConfig);
+
+    for (String resource : resources) {
+      IdealState is = accessor.getProperty(accessor.keyBuilder().idealStates(resource));
+      setSingleIdealState(is);
+
+      Map<String, List<String>> partitionMap = new HashMap<>();
+      for (int p = 0; p < nPartition; p++) {
+        Partition partition = new Partition(resource + "_" + p);
+        for (int r = 0; r < nReplica; r++) {
+          String instanceName = HOSTNAME_PREFIX + r;
+
+          // PartitionMap is used as a preferenceList.
+          partitionMap.put(partition.getPartitionName(), Collections.singletonList(instanceName));
+          if (p == 0) {
+            // Dont set current state. set best possible on another node
+            // Set a pending message to drop a replica that doesn't exist in currentState
+            currentStateOutput.setPendingMessage(resource, partition, instanceName,
+                generateMessage("OFFLINE", "DROPPED", instanceName));
+            // Set pending message to bootstrap elsewhere
+            String dummyInstance = "dummy_instance";
+            bestPossibleStateOutput.setState(resource, partition, dummyInstance, "ONLINE");
+            messageSelectOutput.addMessage(resource, partition,
+                generateMessage("OFFLINE", "ONLINE", dummyInstance));
+            expectedResult.setState(resource, partition, dummyInstance, "ONLINE");
+          } else {
+            currentStateOutput.setCurrentState(resource, partition, instanceName, "ONLINE");
+            bestPossibleStateOutput.setState(resource, partition, instanceName, "ONLINE");
+            expectedResult.setState(resource, partition, instanceName, "ONLINE");
+          }
+        }
+      }
+      bestPossibleStateOutput.setPreferenceLists(resource, partitionMap);
+    }
+
+    event.addAttribute(AttributeName.BEST_POSSIBLE_STATE.name(), bestPossibleStateOutput);
+    event.addAttribute(AttributeName.MESSAGES_SELECTED.name(), messageSelectOutput);
+    event.addAttribute(AttributeName.CURRENT_STATE.name(), currentStateOutput);
+    event.addAttribute(AttributeName.CURRENT_STATE_EXCLUDING_UNKNOWN.name(), currentStateOutput);
+    event.addAttribute(AttributeName.ControllerDataProvider.name(), new ResourceControllerDataProvider());
+    runStage(event, new ReadClusterDataStage());
+    runStage(event, new IntermediateStateCalcStage());
+
+    IntermediateStateOutput output = event.getAttribute(AttributeName.INTERMEDIATE_STATE.name());
+
+    for (String resource : resources) {
+      // Note Assert.assertEquals won't work. If "actual" is an empty map, it won't compare
+      // anything.
+      Assert.assertTrue(output.getPartitionStateMap(resource)
+          .getStateMap()
+          .equals(expectedResult.getPartitionStateMap(resource).getStateMap()));
+    }
+  }
+
   private void preSetup(String[] resources, int numOfLiveInstances, int numOfReplicas) {
     setupIdealState(numOfLiveInstances, resources, numOfLiveInstances, numOfReplicas,
         IdealState.RebalanceMode.FULL_AUTO, "OnlineOffline");