Node.js MongoDB collection.find().toArray não retorna nada

function getUsers () {
  return new Promise(function(resolve, reject) {
     database.collection("customers").find().toArray( function(err, docs) {
      if (err) {
        // Reject the Promise with an error
        return reject(err)
      }

      // Resolve (or fulfill) the promise with data
      return resolve(docs)
    })
  })
}