Unbeatable Tic-Tac-Toe

Select	Select	Select
Select	O	Select
Select	Select	X

Fatal error: Uncaught Error: Call to a member function getElementsByTagName() on null in /usr/local/www/apache24/data/tictactoe/index.php:38 Stack trace: #0 /usr/local/www/apache24/data/tictactoe/index.php(113): update_element('t9075', 'moves', '____O___X') #1 /usr/local/www/apache24/data/tictactoe/index.php(334): generate('____O___X', 't9075') #2 {main} thrown in /usr/local/www/apache24/data/tictactoe/index.php on line 38