Fix fast last empty cache handling

Author: Caideyipi

external-service-impl/rest/src/main/java/org/apache/iotdb/rest/protocol/v2/impl/RestApiServiceImpl.java

@@ -34,6 +34,7 @@
 import org.apache.iotdb.db.queryengine.plan.execution.ExecutionResult;
 import org.apache.iotdb.db.queryengine.plan.execution.IQueryExecution;
 import org.apache.iotdb.db.queryengine.plan.parser.StatementGenerator;
+import org.apache.iotdb.db.queryengine.plan.relational.metadata.fetcher.cache.TableDeviceLastCache;
 import org.apache.iotdb.db.queryengine.plan.relational.metadata.fetcher.cache.TableDeviceSchemaCache;
 import org.apache.iotdb.db.queryengine.plan.relational.metadata.fetcher.cache.TableId;
 import org.apache.iotdb.db.queryengine.plan.statement.Statement;
@@ -196,6 +197,10 @@ public Response executeFastLastQueryStatement(
           for (final Map.Entry<String, Pair<TSDataType, TimeValuePair>> measurementLastEntry :
               device2MeasurementLastEntry.getValue().entrySet()) {
             final TimeValuePair tvPair = measurementLastEntry.getValue().getRight();
+            if (tvPair == TableDeviceLastCache.PLACEHOLDER_EMPTY_COLUMN
+                || tvPair.getValue() == null) {
+              continue;
+            }
             valueList.add(tvPair.getValue().getStringValue());
             dataTypeList.add(tvPair.getValue().getDataType().name());
             targetDataSet.addTimestampsItem(tvPair.getTimestamp());

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/thrift/impl/ClientRPCServiceImpl.java

@@ -1399,7 +1399,8 @@ public TSExecuteStatementResp executeFastLastDataQueryForOneDeviceV2(
             if (timeValuePair == null) {
               allCached = false;
               break;
-            } else if (timeValuePair.getValue() == null) {
+            } else if (timeValuePair == TableDeviceLastCache.PLACEHOLDER_EMPTY_COLUMN
+                || timeValuePair.getValue() == null) {
               // there is no data for this sensor
               if (!canUseNullEntry) {
                 allCached = false;