[To rel/0.12][IOTDB-2008] Fix null result bug of GROUP BY FILL query

cluster/src/main/java/org/apache/iotdb/cluster/query/LocalQueryExecutor.java

@@ -821,13 +821,20 @@ public List<ByteBuffer> getGroupByResult(long executorId, long startTime, long e
     return resultBuffers;
   }
 
+  /**
+   * returns a non-nul ByteBuffer as thrift response, which not allows null objects. If the
+   * ByteBuffer data equals <0, null>, it means that the NextNotNullValue is null.
+   */
   public ByteBuffer peekNextNotNullValue(long executorId, long startTime, long endTime)
       throws ReaderNotFoundException, IOException {
     GroupByExecutor executor = queryManager.getGroupByExecutor(executorId);
     if (executor == null) {
       throw new ReaderNotFoundException(executorId);
     }
     Pair<Long, Object> pair = executor.peekNextNotNullValue(startTime, endTime);
+    if (pair == null) {
+      pair = new Pair<>(0L, null);
+    }
     ByteBuffer resultBuffer;
     ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
     try (DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream)) {

cluster/src/main/java/org/apache/iotdb/cluster/query/groupby/RemoteGroupByExecutor.java

@@ -160,7 +160,9 @@ public Pair<Long, Object> peekNextNotNullValue(long nextStartTime, long nextEndT
     if (aggrBuffer != null) {
       long time = aggrBuffer.getLong();
       Object o = SerializeUtils.deserializeObject(aggrBuffer);
-      result = new Pair<>(time, o);
+      if (o != null) {
+        result = new Pair<>(time, o);
+      }
     }
     logger.debug(
         "Fetched peekNextNotNullValue from {} of [{}, {}]: {}",

cluster/src/main/java/org/apache/iotdb/cluster/query/last/ClusterLastQueryExecutor.java

@@ -74,7 +74,7 @@ public ClusterLastQueryExecutor(LastQueryPlan lastQueryPlan, MetaGroupMember met
   }
 
   @Override
-  protected List<Pair<Boolean, TimeValuePair>> calculateLastPairForSeries(
+  public List<Pair<Boolean, TimeValuePair>> calculateLastPairForSeries(
       List<PartialPath> seriesPaths,
       List<TSDataType> dataTypes,
       QueryContext context,

server/src/main/java/org/apache/iotdb/db/query/dataset/groupby/GroupByFillDataSet.java

@@ -45,6 +45,7 @@
 public class GroupByFillDataSet extends QueryDataSet {
 
   private GroupByEngineDataSet groupByEngineDataSet;
+  private final LastQueryExecutor lastQueryExecutor;
   private Map<TSDataType, IFill> fillTypes;
   // the first value for each time series
   private Object[] previousValue;
@@ -60,10 +61,12 @@ public GroupByFillDataSet(
       GroupByEngineDataSet groupByEngineDataSet,
       Map<TSDataType, IFill> fillTypes,
       QueryContext context,
-      GroupByTimeFillPlan groupByFillPlan)
+      GroupByTimeFillPlan groupByFillPlan,
+      LastQueryExecutor lastQueryExecutor)
       throws StorageEngineException, IOException, QueryProcessException {
     super(new ArrayList<>(paths), dataTypes, groupByFillPlan.isAscending());
     this.groupByEngineDataSet = groupByEngineDataSet;
+    this.lastQueryExecutor = lastQueryExecutor;
     this.fillTypes = fillTypes;
     List<StorageGroupProcessor> list = StorageEngine.getInstance().mergeLock(paths);
     try {
@@ -125,8 +128,8 @@ private void initLastTimeArray(QueryContext context, GroupByTimeFillPlan groupBy
       seriesPaths.add((PartialPath) paths.get(i));
     }
     List<Pair<Boolean, TimeValuePair>> lastValueContainer =
-        LastQueryExecutor.calculateLastPairForSeriesLocally(
-            seriesPaths, dataTypes, context, null, groupByFillPlan.getDeviceToMeasurements());
+        lastQueryExecutor.calculateLastPairForSeries(
+            seriesPaths, dataTypes, context, null, groupByFillPlan);
     for (int i = 0; i < lastValueContainer.size(); i++) {
       if (Boolean.TRUE.equals(lastValueContainer.get(i).left)) {
         lastTimeArray[i] = lastValueContainer.get(i).right.getTimestamp();

server/src/main/java/org/apache/iotdb/db/query/executor/LastQueryExecutor.java

@@ -134,7 +134,7 @@ public QueryDataSet execute(QueryContext context, LastQueryPlan lastQueryPlan)
     return dataSet;
   }
 
-  protected List<Pair<Boolean, TimeValuePair>> calculateLastPairForSeries(
+  public List<Pair<Boolean, TimeValuePair>> calculateLastPairForSeries(
       List<PartialPath> seriesPaths,
       List<TSDataType> dataTypes,
       QueryContext context,

server/src/main/java/org/apache/iotdb/db/query/executor/QueryRouter.java

@@ -240,13 +240,16 @@ public QueryDataSet groupByFill(GroupByTimeFillPlan groupByFillPlan, QueryContex
           IOException {
     GroupByEngineDataSet groupByEngineDataSet =
         (GroupByEngineDataSet) groupBy(groupByFillPlan, context);
+    // here we pass an empty LastQueryPlan as we don't depend on it but only to generate a
+    // LastQueryExecutor
     return new GroupByFillDataSet(
         groupByFillPlan.getDeduplicatedPaths(),
         groupByFillPlan.getDeduplicatedDataTypes(),
         groupByEngineDataSet,
         groupByFillPlan.getFillType(),
         context,
-        groupByFillPlan);
+        groupByFillPlan,
+        getLastQueryExecutor(new LastQueryPlan()));
   }
 
   @Override