diff --git a/src/benchCsv.c b/src/benchCsv.c
index ac2e7cb9..34e0ba7b 100644
--- a/src/benchCsv.c
+++ b/src/benchCsv.c
@@ -293,7 +293,7 @@ int32_t genRowByField(char* buf, BArray* fields, int16_t fieldCnt, char* binanry
       }
     }
 
-    pos1 += dataGenByField(fd, buf, pos1, prefix, k);
+    pos1 += dataGenByField(fd, buf, pos1, prefix, k, "");
   }
   
   return pos1;
diff --git a/src/benchDataMix.c b/src/benchDataMix.c
index d819ec9f..d2f59e7b 100644
--- a/src/benchDataMix.c
+++ b/src/benchDataMix.c
@@ -14,8 +14,6 @@
 #include "benchDataMix.h"
 #include <float.h>
 
-#define VAL_NULL "NULL"
-
 #define VBOOL_CNT 3
 
 int32_t inul = 20; // interval null count
@@ -97,11 +95,11 @@ uint32_t genRadomString(char* val, uint32_t len, char* prefix) {
 
 
 // data row generate by randowm
-uint32_t dataGenByField(Field* fd, char* pstr, uint32_t len, char* prefix, int64_t *k) {
+uint32_t dataGenByField(Field* fd, char* pstr, uint32_t len, char* prefix, int64_t *k, char* nullVal) {
     uint32_t size = 0;
-    char val[512] = VAL_NULL;
+    char val[512] = {0};
     if( fd->fillNull && RD(inul) == 0 ) {
-        size = sprintf(pstr + len, ",%s", VAL_NULL);
+        size = sprintf(pstr + len, ",%s", nullVal);
         return size;
     }
 
diff --git a/src/benchInsertMix.c b/src/benchInsertMix.c
index 3e62143e..87ac2670 100644
--- a/src/benchInsertMix.c
+++ b/src/benchInsertMix.c
@@ -285,6 +285,8 @@ uint32_t appendRowRuleOld(SSuperTable* stb, char* pstr, uint32_t len, int64_t ti
 }
 
 #define GET_IDX(i) info->batCols[i]
+#define VAL_NULL "NULL"
+
 uint32_t genRowMixAll(threadInfo* info, SSuperTable* stb, char* pstr, uint32_t len, int64_t ts, int64_t* k) {
   uint32_t size = 0;
   // first col is ts
@@ -317,7 +319,7 @@ uint32_t genRowMixAll(threadInfo* info, SSuperTable* stb, char* pstr, uint32_t l
       }
     }
 
-    size += dataGenByField(fd, pstr, len + size, prefix, k);
+    size += dataGenByField(fd, pstr, len + size, prefix, k, VAL_NULL);
   }
 
   // end