Page should show exist instead of blank page

Page should show exist instead of blank page

I made login.php file by following video tutorial and I am trying to make
so that the page will show exist instead of blank page. I know that user
exists because I made user with my name on phpMyAdmin.
Her is the code
<?php
include 'core/init.php';
if (user_exists('Denis') === true) {
echo 'exists';
}
die();
if(empty($_POST) === false) {
$username = $_POST['username'];
$password = $_POST['password'];
if (empty($username) === true || empty($password) === true) {
$errors[] = 'You need to enter a username and password';
} else if (user_exists($username) === false) {
$errors[] = 'We can\'t find that username. Have you registered?';
}
}
?>