mongoose 8.8.3 breaks on bulkSave: TypeError: Cannot set properties of undefined (setting '__subdocs')

[O-Q]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.8.3

Node.js version

22

MongoDB server version

8.0.3

Typescript version (if applicable)

5.7.2

Description

I've got this error when I try to bulk save a list of documents:

TypeError: Cannot set properties of undefined (setting '__subdocs')
 at node_modules/.pnpm/mongoose@8.8.3/node_modules/mongoose/lib/plugins/saveSubdocs.js:31:39
node_modules/.pnpm/mongoose@8.8.3/node_modules/mongoose/lib/helpers/each.js:21:16
node_modules/.pnpm/mongoose@8.8.3/node_modules/mongoose/lib/plugins/saveSubdocs.js:27:9
node_modules/.pnpm/kareem@2.6.3/node_modules/kareem/index.js:113:15

Apparently this line was recently added to the source code.

https://github.com/Automattic/mongoose/blame/bb98dcf859b2cf0cc7da9d16d9d09afe445321f3/lib/plugins/saveSubdocs.js#L31

Steps to Reproduce

const subDocSchema = new Schema({ title: { type: String } });

const schema = new Schema({
	name: { type: String, required: true },
	subDoc: { type: subDocSchema }
});

const Task = mongoose.model("task", schema);

const task1 = new Task({ name: "Task 1" });
await task1.save();

const tasks = await Task.find();

for (const task of tasks) {
	task.set({ subDoc: { title: "test" } });
}

await Task.bulkSave(tasks);

Expected Behavior

No response

[vkarpov15]

I wasn't able to repro this issue with the following script:

'use strict';

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

void async function main() {
  await mongoose.connect('mongodb://127.0.0.1:27017/mongoose_test');

  const subDocSchema = new Schema({ title: { type: String } });

  const schema = new Schema({
    name: { type: String, required: true },
    subDoc: { type: subDocSchema }
  });

  const Task = mongoose.model("task", schema);

  const task1 = new Task({ name: "Task 1" });
  await task1.save();

  const tasks = await Task.find();

  for (const task of tasks) {
    task.set({ subDoc: { title: "test" } });
  }

  await Task.bulkSave(tasks);
  console.log('Done');
}();

Not sure why you're getting this error, but it is an easy one-line fix so we'll just fix it.

[rhugie]

I also had this error after 8.8.3 so it's a thing