fix(query): add some check for null pointer.

source/libs/executor/src/sortoperator.c

@@ -67,6 +67,10 @@ SSDataBlock* getSortedBlockData(SSortHandle* pHandle, SSDataBlock* pDataBlock, i
   ASSERT(taosArrayGetSize(pColMatchInfo) == pDataBlock->info.numOfCols);
 
   SSDataBlock* p = tsortGetSortedDataBlock(pHandle);
+  if (p == NULL) {
+    return NULL;
+  }
+
   blockDataEnsureCapacity(p, capacity);
 
   while (1) {

source/libs/executor/src/tsort.c

@@ -553,7 +553,7 @@ static int32_t createInitialSortedMultiSources(SSortHandle* pHandle) {
       }
     }
 
-    if (pHandle->pDataBlock->info.rows > 0) {
+    if (pHandle->pDataBlock != NULL && pHandle->pDataBlock->info.rows > 0) {
       size_t size = blockDataGetSize(pHandle->pDataBlock);
 
       // Perform the in-memory sort and then flush data in the buffer into disk.