TypeError: C:UsersUSERRealtime-Chatplayground-loginviewsindex.pug:3
    1| extends layout
    2| block content
  > 3|   if registrations.length
    4|     table
    5|       tr
    6|         th Name
Cannot read property 'length' of undefined
[...]
at router.get (C:UsersUSERRealtime-Chatplayground-loginroutesindex.js:33:7)
[...]

const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const registrationSchema = new Schema({
//[...]
});
module.exports = mongoose.model('Registration', registrationSchema);

//[...]
const Registration = require('../models/Registration');
//[...]
router.post('/', [{...}], (req, res) => {
//NR1
  const errors = validationResult(req);
  if(errors.isEmpty()) {
//NR2
    const registration = new Registration(req.body);
    registration.save()
      .then(() => {res.send('Thanks for your registration!')})
      .catch(() => {res.send('Sorry! Something went wrong.')})
  } else {
    res.render('form', {
      title: 'Registration form',
      errors: errors.array(),
      data: req.body
  });
//NR3
  };
});
router.get('/registrations', (req, res) => {
  Registration.find()
    .then((registrations) => {
        res.render('index', {title: 'Listing registrations', registrations})})
    .catch(() => {res.send('Sorry! Something went wrong.')});
})
//[...]

extends layout
block content
  if registrations
    table
      tr
        th Name
        th Email
      each registration in registrations
        tr
          td= registrations.name
          td= registrations.email
  else
    p No registrations yet :(