Fatal error: Uncaught TypeError: isBookLikedByUser(): Argument #2 ($user_id) must be of type int, null given, called in /home/xs249675/comic-mob.com/public_html/book/book.php on line 29 and defined in /home/xs249675/comic-mob.com/public_html/book/book-helper.php:103 Stack trace: #0 /home/xs249675/comic-mob.com/public_html/book/book.php(29): isBookLikedByUser(Object(PDO), NULL, 51) #1 {main} thrown in /home/xs249675/comic-mob.com/public_html/book/book-helper.php on line 103