Two questions... 1. How you can improve this code? 2. Do you validate the param is available?

express-server.js

app.get('/users/:id', (req, res) => {
  const userId = req.params.id
  if (!userId) {
    return res.sendStatus(400).json({
      error: 'Missing id'
    })
  }
  Users.get(userId, (err, user) => {
    if (err) {
      return res.sendStatus(500).json(err)
    }
    res.send(users)
  })
})