Avoid sending empty `projection` option with queries

[vkarpov15]

Prerequisites

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

Mongoose version

6.9.1

Node.js version

16.x

MongoDB server version

Any

Typescript version (if applicable)

No response

Description

The following script shows that Mongoose sends projection: {} to the MongoDB driver, which is unnecessary. Would be ideal if Mongoose didn't set a projection option if the projection is empty.

'use strict';

const mongoose = require('mongoose');
mongoose.set('debug', true);

run().catch(err => console.log(err));

async function run() {
  await mongoose.connect('mongodb://localhost:27017/test');
  const schema = new mongoose.Schema({ name: String });
  const Test = mongoose.model('Test', schema);

  // Prints "Mongoose: tests.findOne({}, { projection: {} })"
  await Test.findOne(); // Sends `projection: {}` to MongoDB
}

Steps to Reproduce

See above

Expected Behavior

No response