Check empty fields on mongoose
<p>I have this function on my node REST API </p>

<pre><code>var router = express.Router();

/*router.get('/getUsers', function(req, res) {
    res.json({ message: 'hooray! welcome to our api!' });
});*/

router.route('/Users')
  .get(function(req,res){
      User.find(function(err,users){
        if(err)
          res.send(err);

        console.log('GET request');
        res.json(users);
      });
})
  .post(function(req,res){
      var user = new User();
      user.name = req.body.name;
      user.lastName = req.body.lastName;

      if(!user.name || !user.lastName){
        user.save(function(err){
          if(err)
            res.send(err);

          console.log('POST request');
          res.json({message:'Usuario creado'});
        });
      }else{
        res.json({message:'Campos vacíos'});
      }

  });
</code></pre>

<p>It works but when I a send a POST  request with empty parameters it saves a document in mongoDB without the <code>name</code> and <code>lastName</code> fields and <code>if(!user.name || !user.lastName)</code> doesn't work to avoid it</p>