Merge pull request #20596 from taosdata/szhou/python-udf

fix: aggregate function can return null value

source/libs/function/src/tudf.c

@@ -1209,6 +1209,10 @@ int32_t udfAggFinalize(struct SqlFunctionCtx *pCtx, SSDataBlock *pBlock) {
   if (udfCallCode != 0) {
     fnError("udfAggFinalize error. doCallUdfAggFinalize step. udf code:%d", udfCallCode);
     GET_RES_INFO(pCtx)->numOfRes = 0;
+  } else {
+    if (resultBuf.numOfResult == 0) {
+      udfRes->finalResNum = 0;
+      GET_RES_INFO(pCtx)->numOfRes = 0;
     } else {
       if (resultBuf.bufLen <= session->bytes) {
         memcpy(udfRes->finalResBuf, resultBuf.buf, resultBuf.bufLen);
@@ -1220,6 +1224,7 @@ int32_t udfAggFinalize(struct SqlFunctionCtx *pCtx, SSDataBlock *pBlock) {
         udfCallCode = TSDB_CODE_UDF_INVALID_OUTPUT_TYPE;
       }
     }
+  }
 
   freeUdfInterBuf(&resultBuf);