PDO returns false instead of empty array

I am using PHP 7.4 and my class have a function that should return an array. But if the row is empty it returns false instead of an empty array. That is why I get an error message:

Return value must be of type array, bool returned

private function getCartItem(int $sku): array
{
    $statement = $this->pdo->prepare("SELECT * FROM pbo_cartItem WHERE cartId = ? AND sku = ?");
    $statement->execute(array($this->cartId, $sku));
    return $statement->fetch(PDO::FETCH_ASSOC);
}