Warning: PDO::prepare(): SQLSTATE[00000]: No error: PDO constructor was not called in /volume2/web/iteach4u/htdocs/2017/_lib/db_iteach4u.php on line 22

Fatal error: Uncaught Error: Call to a member function execute() on null in /volume2/web/iteach4u/htdocs/2017/_lib/db_iteach4u.php:23
Stack trace:
#0 /volume2/web/iteach4u/htdocs/2017/_lib/config.php(237): include_once()
#1 /volume2/web/iteach4u/htdocs/php/__config.php(3): include_once('/volume2/web/it...')
#2 /volume2/web/iteach4u/htdocs/php/oauth2/login/start.php(11): include('/volume2/web/it...')
#3 {main}
  thrown in /volume2/web/iteach4u/htdocs/2017/_lib/db_iteach4u.php on line 23