Query middleware hook is being fired by "init"

[jayadrathamondal]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
Middleware "init" is a document middleware. But fires for the following hook where I have specifically added document: false.

const postHook = function (error, docs, next) {
    console.log(`postHook -> error, docs, next`, error, docs, next)
    if (error) {
        // Transform the error
    }
    next(error);
};

schema.post(/^\w+/, { query: true, document: false }, postHook);

If the current behavior is a bug, please provide the steps to reproduce.

Use the above hook for any schema and then do any query like following.

const emp = await EmployeeModel.create(EmpData);
await EmployeeModel.findById(emp.id);

This will give error TypeError: next is not a function
And see there is a console log in the postHook which gives following.

postHook -> error, docs, next {
      _id: 5f32efb10c0e5b5ad79d601d,
      name: 'Full Name',
      username: 'Emp_1',
      bio: 'He is Employee-Emp_1',
      email: 'emp_1@domain.com',
      age: 28,
      countryCode: 'IND',
      createdAt: 2020-08-11T19:21:21.398Z,
      updatedAt: 2020-08-11T19:21:21.398Z,
      __v: 0,
  } undefined undefined

In which above log its clear that the next is undefined & error is the document itself. This should not be the case for an error handler hook.
As per doc init hooks are synchronous and doesn't receive next as a parameter.
So I thought may be after findById the hook is being fired. So I changed the regexp where I'm adding the postHook in the schema, with the following.

schema.post(/^!i\w+$/, { query: true, document: false }, postHook);

This just says, for all which not starts with "i". And now the error is gone. So I'm thinking that for the init middleware the hook is being fired.

What is the expected behavior?
Middleware "init" is a document middleware. Should not fire when I'm adding hook for only query middleware..

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
nodejs@14.4.0
mongoose@5.9.28
mongodb@4.2.6