Internal Server Error

MartiniError: Trying to get property of non-object

    in /var/www/html/martini-git/src/Newsquest/Modules/EmailBulletinModule.php at line 421

#0 /var/www/html/martini-git/src/Newsquest/Modules/EmailBulletinModule.php(421): ErrorHandler::handleError(8, 'Trying to get p...', '/var/www/html/m...', 421, Array)
#1 /var/www/html/martini-git/src/Newsquest/Modules/EmailBulletinModule.php(399): Newsquest\Modules\EmailBulletinModule->populateBulletinPreviewPage()
#2 /var/www/html/martini-git/src/core/ModuleController.php(229): Newsquest\Modules\EmailBulletinModule->generateBulletin(Object(HttpRequest), Array)
#3 /var/www/html/martini-git/src/core/ModuleController.php(181): ModuleController->callAction('generatebulleti...', Object(HttpRequest))
#4 /var/www/html/martini-git/src/core/ModuleController.php(58): ModuleController->handleRequest(Object(HttpRequest))
#5 /var/www/html/martini-git/src/web.php(626): ModuleController->handleDisplayRequest(Object(HttpRequest))
#6 /var/www/html/martini-git/src/web.php(107): RequestHandler->handleRequestInternal(Object(HttpRequest))
#7 /var/www/html/martini-git/lib/http.php(77): RequestHandler->handleRequest(Object(HttpRequest))
#8 /var/www/html/martini-git/htdocs/index.php(155): HttpApplication->run()
#9 {main}