resolve the NPE problem (apache#15646)

Author: zerolbsony

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/memtable/WritableMemChunkGroup.java

@@ -54,7 +54,7 @@ public void writeTablet(
       int end,
       TSStatus[] results) {
     for (int i = 0; i < columns.length; i++) {
-      if (columns[i] == null) {
+      if (columns[i] == null || schemaList.get(i) == null) {
         continue;
       }
       IWritableMemChunk memChunk = createMemChunkIfNotExistAndGet(schemaList.get(i));
@@ -97,7 +97,7 @@ public boolean contains(String measurement) {
   @Override
   public void writeRow(long insertTime, Object[] objectValue, List<IMeasurementSchema> schemaList) {
     for (int i = 0; i < objectValue.length; i++) {
-      if (objectValue[i] == null) {
+      if (objectValue[i] == null || schemaList.get(i) == null) {
         continue;
       }
       IWritableMemChunk memChunk = createMemChunkIfNotExistAndGet(schemaList.get(i));