Check out example codes for "mongodb node findone how to handle no results using promises". It will help you in understanding the concepts better.

Code Example 1

const findUser = async function (params) { 
    try {  return await User.findOne(params)
    } catch(err) { console.log(err) }
}

const userSteve = findUser({firstName: Steve})

Code Example 2

const assert = require('assert');

schema.static('findMinOne', function(conditions) {
  return this.find(conditions).then(res => assert.ok(res.length >= 1, 'No documents found'));
});

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