diff --git a/pkg/is/is.go b/pkg/is/is.go
index 379dd93..61bd3af 100644
--- a/pkg/is/is.go
+++ b/pkg/is/is.go
@@ -286,7 +286,7 @@ func Longitude[T any](t T) bool {
 // JSON is the validation function for validating if the current field's value is a valid json string.
 func JSON[T any](t T) bool {
 	rv := reflect.ValueOf(t)
-	if rv.Type() == bytesType {
+	if rv.Type() == nilType {
 		return json.Valid(rv.Bytes())
 	}
 	if rv.Kind() == reflect.String {
diff --git a/pkg/is/util.go b/pkg/is/util.go
index 3d180e8..421c93d 100644
--- a/pkg/is/util.go
+++ b/pkg/is/util.go
@@ -16,7 +16,7 @@ var (
 	ErrBadRange = errors.New("bad value range")
 
 	timeType = reflect.TypeOf(time.Time{})
-	//nilType  = reflect.TypeOf([]byte(nil))
+	nilType  = reflect.TypeOf([]byte(nil))
 )
 
 // convert value to float64, return error on failed