fix: udf2 reuse old state when new input is null

source/libs/function/test/udf2.c

@@ -26,7 +26,7 @@ int32_t udf2_start(SUdfInterBuf *buf) {
 
 int32_t udf2(SUdfDataBlock* block, SUdfInterBuf *interBuf, SUdfInterBuf *newInterBuf) {
   double sumSquares = *(double*)interBuf->buf;
-  int8_t numOutput = 0;
+  int8_t numNotNull = 0;
   for (int32_t i = 0; i < block->numOfCols; ++i) {
     SUdfColumn* col = block->udfCols[i];
     if (!(col->colMeta.type == TSDB_DATA_TYPE_INT || 
@@ -56,15 +56,18 @@ int32_t udf2(SUdfDataBlock* block, SUdfInterBuf *interBuf, SUdfInterBuf *newInte
         default: 
           break;
       }
-      numOutput = 1;
+      ++numNotNull;
     }
   }
 
-  if (numOutput == 1) {
-    *(double*)(newInterBuf->buf) = sumSquares;
-    newInterBuf->bufLen = sizeof(double);
+  *(double*)(newInterBuf->buf) = sumSquares;
+  newInterBuf->bufLen = sizeof(double);
+
+  if (interBuf->numOfResult == 0 && numNotNull == 0) {
+    newInterBuf->numOfResult = 0;
+  } else {
+    newInterBuf->numOfResult = 1;
   }
-  newInterBuf->numOfResult = numOutput;
   return 0;
 }