message: API: Fix undefined Course chatRooms id extraction
diff: @@ -121,10 +121,12 @@ const courseSchema = new mongoose.Schema({
  }
  }
  + if (ret.chatRooms) {
  ret.chatRooms = ret.chatRooms.map(extractMongoId);
  }
  }
  }
  + }
  );
  courseSchema.pre('save', async function () {
  