fix(query): avoid sending unnecessary empty projection to MongoDB server

[vkarpov15]

Fix #13050

Summary

Right now we always send projection option to the MongoDB server, even if projection is an empty object. This is a bit clunky for numerous reasons: perf, messy logs, etc. With this change, we won't send projection if it is an empty object.

Examples

No projections in below script:

'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);

  await Test.findOne();

  await Test.find();

  await Test.findOneAndUpdate({}, { name: 'bar' });
}

[AbdelrahmanHafez]

Other than the missing tests for this, LGTM. 👍
We could test this using sinon.spy(...).

[Uzlopak]

makes sense, but should have a unit test.

[vkarpov15]

Would be nice to have a test, I opened an issue to track.