Save as empty string for not nullable nil field serialized into json

schema/serializer.go

@@ -101,6 +101,9 @@ func (JSONSerializer) Scan(ctx context.Context, field *Field, dst reflect.Value,
 func (JSONSerializer) Value(ctx context.Context, field *Field, dst reflect.Value, fieldValue interface{}) (interface{}, error) {
 	result, err := json.Marshal(fieldValue)
 	if string(result) == "null" {
+		if field.TagSettings["NOT NULL"] != "" {
+			return "", nil
+		}
 		return nil, err
 	}
 	return string(result), err

tests/serializer_test.go

@@ -19,6 +19,7 @@ type SerializerStruct struct {
 	Name                   []byte                 `gorm:"json"`
 	Roles                  Roles                  `gorm:"serializer:json"`
 	Roles2                 *Roles                 `gorm:"serializer:json"`
+	Roles3                 *Roles                 `gorm:"serializer:json;not null"`
 	Contracts              map[string]interface{} `gorm:"serializer:json"`
 	JobInfo                Job                    `gorm:"type:bytes;serializer:gob"`
 	CreatedTime            int64                  `gorm:"serializer:unixtime;type:time"` // store time in db, use int as field type
@@ -109,7 +110,7 @@ func TestSerializer(t *testing.T) {
 	}
 
 	var result SerializerStruct
-	if err := DB.Where("roles2 IS NULL").First(&result, data.ID).Error; err != nil {
+	if err := DB.Where("roles2 IS NULL AND roles3 = ?", "").First(&result, data.ID).Error; err != nil {
 		t.Fatalf("failed to query data, got error %v", err)
 	}