Fatal error: Uncaught Error: Call to a member function query() on null in /www/wwwroot/library/DbPdoMysql.class.php:137 Stack trace: #0 /www/wwwroot/library/DbPdoMysql.class.php(261): DbPdoMysql->querySql('SELECT * FROM t...') #1 /www/wwwroot/baixian/bx_mobile/models/AnswerModel.class.php(187): DbPdoMysql->getMoreSelect('tb_bill', '*', 'WHERE Fid>0') #2 /www/wwwroot/baixian/bx_mobile/controllers/BaseController.php(327): AnswerModel->getAdsList('WHERE Fid>0') #3 /www/wwwroot/baixian/bx_mobile/controllers/TeacherController.php(31): BaseController::setUiPath() #4 /www/wwwroot/baixian/bx_mobile/controllers/Teacher/Tfriend.class.php(13): TeacherController->_run() #5 /www/wwwroot/baixian/bx_mobile/start/index.php(14): Tfriend->__construct() #6 {main} thrown in /www/wwwroot/library/DbPdoMysql.class.php on line 137