Expected to return a value at the end of arrow function when connecting to MongoDB

I am getting the eslint error:

[eslint] Expected to return a value at the end of arrow function. [consistent-return]

I've checked and each path has a return statement. But I feel like my callback function is throwing it for a loop?

Here's the code:

let db;
module.exports.initDb = (callback) => {

if (db) {

return callback(null, db);

MongoClient.connect(process.env.MONGO_URL, { useNewUrlParser: true }, (err, client) => {

if (err) {

return callback(err);

db = client.db('partsync');