Fatal error: Uncaught exception Exception with message File assets/css/basic.css does not exist thrown in system/modules/core/library/Contao/Combiner.php on line 136

#0 system/modules/core/library/Contao/Controller.php(1887): Contao\Combiner->add('assets/css/basi...', '1515010669', 'all')
#1 system/modules/core/classes/FrontendTemplate.php(99): Contao\Controller::replaceDynamicScriptTags('...')
#2 system/modules/core/pages/PageRegular.php(183): Contao\FrontendTemplate->output(true)
#3 index.php(263): Contao\PageRegular->generate(Object(Contao\PageModel), true)
#4 index.php(447): Index->run()
#5 {main}