Error Detected

In file: /var/www/online-magazine.nl/production/magazine/vendor/zendframework/zendframework1/library/Zend/Log/Writer/Stream.php On line: 81 Code: 0 Trace error: #0 /var/www/online-magazine.nl/production/magazine/docs/classes/error/ErrorReporter.php(92): Zend_Log_Writer_Stream->__construct(false) #1 /var/www/online-magazine.nl/production/magazine/docs/classes/error/ErrorReporter.php(106): ErrorReporter::logError(Array, '/var/www/online...', 141, '') #2 /var/www/online-magazine.nl/production/magazine/docs/classes/nl/blueberry/magazine/frontend/UserHandler.php(141): ErrorReporter::reportError(101, '/var/www/online...', 141, '') #3 /var/www/online-magazine.nl/production/magazine/docs/session.php(124): nl\blueberry\magazine\frontend\UserHandler->getUser() #4 /var/www/online-magazine.nl/production/magazine/docs/index.php(75): require('/var/www/online...') #5 {main} Message error: "" cannot be opened with mode "a"