Cannot read property 'addEventListener' of null at

Вот код,

moment.locale('en');
console.log(moment(1316116057189).fromNow());
console.log(moment.locales());
var input = document.querySelector('.c-datepicker-input');
var picker = new MaterialDatePicker().on('submit', function (val) {
  input.value = val.format("DD/MM/YYYY");
});
input.addEventListener('focus', function () {
  return picker.open();
});

Почему пишет ошибку?

Uncaught TypeError: Cannot read property 'addEventListener' of null at