diff --git a/contrib/dolphin/expected/json_object.out b/contrib/dolphin/expected/json_object.out
index e479bb62b586ae733b6c0d67ae6dee0f8c9cc4fd..a84954277f8d774d5d1bfe1fa39c6d74ee23f946 100644
--- a/contrib/dolphin/expected/json_object.out
+++ b/contrib/dolphin/expected/json_object.out
@@ -422,6 +422,14 @@ select json_object('{a,b,"a b c"}', '{a,1,1}');
  {"a" : "a", "b" : "1", "a b c" : "1"}
 (1 row)
 
+reset dolphin.b_compatibility_mode;
+-- unknown 类型之外的null value 
+select json_object('City', 'Cairns', 'Population', DATE_FORMAT(null, '%Y-%m-%d'));
+              json_object               
+----------------------------------------
+ {"City": "Cairns", "Population": null}
+(1 row)
+
 drop schema test_json_object cascade;
 NOTICE:  drop cascades to 3 other objects
 DETAIL:  drop cascades to table tab_json1
diff --git a/contrib/dolphin/plugin_utils/adt/json.cpp b/contrib/dolphin/plugin_utils/adt/json.cpp
index 2783fe3aa2b01ae25b42bc3aa21e90d6494dde15..5d9f3b836697c978d4f0259c22288ecc47f004b2 100644
--- a/contrib/dolphin/plugin_utils/adt/json.cpp
+++ b/contrib/dolphin/plugin_utils/adt/json.cpp
@@ -2286,7 +2286,6 @@ Datum json_object_mysql(PG_FUNCTION_ARGS)
     Oid castfunc = InvalidOid;
     char *outputstr = NULL;
     StringInfo tempstr;
-    bool is_null = false;
     for (i = 0; i < cnt; i++) {
         if (PG_ARGISNULL(i * 2)) {
             ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("arg %d: key cannot be null", 2 * i + 1)));
@@ -2355,7 +2354,6 @@ Datum json_object_mysql(PG_FUNCTION_ARGS)
     result = makeStringInfo();
     appendStringInfoChar(result, '{');
     for (i = 0; i < nargs; i += 2) {
-        is_null = false;
         order = i / 2;
         if (isValid[pos[order]] == false) {
             continue;
@@ -2372,7 +2370,6 @@ Datum json_object_mysql(PG_FUNCTION_ARGS)
             val_type = TEXTOID;
             if (PG_ARGISNULL(2 * pos[order] + 1)) {
                 arg = (Datum)0;
-                is_null = true;
             } else {
                 arg = CStringGetTextDatum(PG_GETARG_POINTER(2 * pos[order] + 1));
             }
@@ -2383,7 +2380,7 @@ Datum json_object_mysql(PG_FUNCTION_ARGS)
             ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("arg %d: could not determine data type", 2 * pos[order] + 2)));
         }
-        add_json(arg, is_null, result, val_type, false);
+        add_json(arg, PG_ARGISNULL(2 * pos[order] + 1), result, val_type, false);
     }
     appendStringInfoChar(result, '}');
     for (int i = 0; i < cnt; i++) {
diff --git a/contrib/dolphin/sql/json_object.sql b/contrib/dolphin/sql/json_object.sql
index b68fbb64e1e1bcc22c44b2bc87b06ced0cab035d..75e6b60bc3a24aedb758a8d5e5ea8ddb231820b6 100644
--- a/contrib/dolphin/sql/json_object.sql
+++ b/contrib/dolphin/sql/json_object.sql
@@ -123,6 +123,9 @@ select json_object(data, my_text) from tab_json2;
 set dolphin.b_compatibility_mode = 0;
 select json_object('{a,1,b,2,3,NULL,"d e f","a b c"}');
 select json_object('{a,b,"a b c"}', '{a,1,1}');
+reset dolphin.b_compatibility_mode;
+-- unknown 类型之外的null value 
+select json_object('City', 'Cairns', 'Population', DATE_FORMAT(null, '%Y-%m-%d'));
 
 drop schema test_json_object cascade;
 reset current_schema;
\ No newline at end of file