message: Fix course ObjectId transforms
diff: @@ -41,8 +41,7 @@ const courseSchema = new mongoose.Schema({
  timestamps: true,
  toObject: {
  transform: function(doc: any, ret: any) {
  - ret._id = ret.id;
  - delete ret.id;
  + ret._id = ret._id.toString();
  }
  }
  }
  