在购物车会话中查看购物车商品错误在布尔值上调用成员函数fetch_assoc（）

Question

I have some basic shopping cart code to display all items in my carts session, the view_cart.php is displaying the error:

Fatal error: Uncaught Error: Call to a member function fetch_assoc() on boolean in C:\wamp64\www\shopping_cart\shopping_cart\view_cart.php on line 72

I have only edited the index a little the code was working perfectly before, now I just can't seem to get rid of this error..?

this is line 72: I cant see the error: ..

<?php
//initialize total
$total = 0;
if (!empty($_SESSION['cart'])){    
    //connection
    $conn = new mysqli('localhost', 'root', '', 'database');
    //create array of initail qty which is 1
    $index = 0;
    if (!isset($_SESSION['qty_array'])) {
        $_SESSION['qty_array'] = array_fill(0, count($_SESSION['cart']), 1);
    }
    $sql = "SELECT * FROM products WHERE id IN (" . implode(',', $_SESSION['cart']) . ")";
    $query = $conn->query($sql);
    while ($row = $query->fetch_assoc()){
    ?>