fix: udf agg can not return null values

source/libs/function/src/tudf.c

@@ -1187,14 +1187,19 @@ int32_t udfAggFinalize(struct SqlFunctionCtx *pCtx, SSDataBlock *pBlock) {
     fnError("udfAggFinalize error. doCallUdfAggFinalize step. udf code:%d", udfCallCode);
     GET_RES_INFO(pCtx)->numOfRes = 0;
   } else {
-    if (resultBuf.bufLen <= session->outputLen) {
-      memcpy(udfRes->finalResBuf, resultBuf.buf, session->outputLen);
-      udfRes->finalResNum = resultBuf.numOfResult;
-      GET_RES_INFO(pCtx)->numOfRes = udfRes->finalResNum;
-    } else {
-      fnError("udfc inter buf size %d is greater than function output size %d", resultBuf.bufLen, session->outputLen);
+    if (resultBuf.numOfResult == 0) {
+      udfRes->finalResNum = 0;
       GET_RES_INFO(pCtx)->numOfRes = 0;
-      udfCallCode = TSDB_CODE_UDF_INVALID_OUTPUT_TYPE;
+    } else {
+      if (resultBuf.bufLen <= session->outputLen) {
+        memcpy(udfRes->finalResBuf, resultBuf.buf, resultBuf.bufLen);
+        udfRes->finalResNum = resultBuf.numOfResult;
+        GET_RES_INFO(pCtx)->numOfRes = udfRes->finalResNum;
+      } else {
+        fnError("udfc inter buf size %d is greater than function output size %d", resultBuf.bufLen, session->bytes);
+        GET_RES_INFO(pCtx)->numOfRes = 0;
+        udfCallCode = TSDB_CODE_UDF_INVALID_OUTPUT_TYPE;
+      }
     }
   }