sdopx\SdopxException: Trying to access array offset on value of type null
    #0 /home/www/vendor/wj008/sdopx/lib/Outer.php(103): sdopx\Sdopx->rethrow()
    #1 /home/www/vendor/wj008/sdopx/Sdopx.php(28): sdopx\lib\Outer->throw()
    #2 /home/www/runtime/file_13bc942826463f79886313daf2126b39course_chapter_tpl.php(40): sdopx\{closure}()
    #3 [internal function]: sdopx\lib\Template->{closure}()
    #4 /home/www/vendor/wj008/sdopx/lib/Template.php(294): call_user_func()
    #5 /home/www/vendor/wj008/sdopx/lib/Template.php(316): sdopx\lib\Template->run()
    #6 /home/www/vendor/wj008/sdopx/lib/Template.php(129): sdopx\lib\Template->runTemplate()
    #7 /home/www/vendor/wj008/sdopx/lib/Template.php(107): sdopx\lib\Template->fetchTpl()
    #8 /home/www/vendor/wj008/sdopx/Sdopx.php(276): sdopx\lib\Template->fetch()
    #9 [internal function]: sdopx\Sdopx->display()
    #10 /home/www/vendor/wj008/beacon/core/View.php(106): call_user_func_array()
    #11 /home/www/vendor/wj008/beacon/core/Controller.php(57): beacon\View->__call()
    #12 /home/www/app/school/controller/Course.php(254): beacon\Controller->display()
    #13 [internal function]: app\school\controller\Course->chapterAction()
    #14 /home/www/vendor/wj008/beacon/core/Route.php(631): ReflectionMethod->invokeArgs()
    #15 /home/www/vendor/wj008/beacon/core/Route.php(744): beacon\Route::runMethod()
    #16 /home/www/www/index.php(87): beacon\Route::run()
    #17 {main}
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