message: Fixed merge issue for object type string
diff: @@ -417,7 +417,7 @@ function updateParentWithParentId(model: Mongoose.Model<any>, meta: MetaData, ob
  }
  else {
  var queryFindCond = {};
  - queryFindCond['_id'] = new Mongoose.mongo.ObjectID(parentId);
  + queryFindCond['_id'] = Utils.getCastObjectId(model, parentId);
  queryFindCond[meta.propertyKey + '._id'] = objs[i]._id;
  let updateMongoOperator = Utils.getMongoUpdatOperatorForRelation(meta);
  let updateSet = {};
  @@ -430,7 +430,7 @@ function updateParentWithParentId(model: Mongoose.Model<any>, meta: MetaData, ob
  Object.keys(parents).forEach(x => {
  if (isJsonMap) {
  var queryFindCond = {};
  - queryFindCond['_id'] = Utils.castToMongooseType(x, Mongoose.Types.ObjectId);
  + queryFindCond['_id'] = Utils.getCastObjectId(model, x);
  bulk.find(queryFindCond).update({ $set: parents[x] });
  }
  else {
  