Stack trace:

#0 /home/salavatgram/public_html/App/Views/main/group.php(15): Core\Error::errorHandler(2, 'Undefined array...', '/home/salavatgr...', 15)
#1 /home/salavatgram/public_html/Core/View.php(28): require('/home/salavatgr...')
#2 /home/salavatgram/public_html/App/Controllers/General.php(383): Core\View::render('main/group.php', Array)
#3 /home/salavatgram/public_html/Core/Router.php(121): App\Controllers\General->group()
#4 /home/salavatgram/public_html/index.php(182): Core\Router->dispatch('group')
#5 {main}

Thrown in '/home/salavatgram/public_html/App/Views/main/group.php' on line 15