Mongoose: `findOne()` returns undefined

Question

I am trying to find a single document from my mongoDB database but it's always returning undefined, but the that document exists in the collection

User.findOne({ discordId: (message.author.id) }, (err, data) => {
    console.log(data) // returns `undefined`
})

The User model

const mongoose = require('mongoose')

const UserSchema = new mongoose.Schema({
    discordId: {
        type: mongoose.Schema.Types.Decimal128,
        required: true,
        unique: true
    },
    playing: {
        type: Boolean
    },
    response: {
        type: String
    },
    points: {
        type: Number
    }
})

module.exports = mongoose.model('User', UserSchema, 'User')