Laravel 5.1.11 在 PHP7 环境上运行 出现的错误 谁帮忙解决一下啊

Fatal error: Uncaught ReflectionException: Class log does not exist in /var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php:737 Stack trace: #0  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php(737): ReflectionClass->__construct('log') #1  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php(627): Illuminate\Container\Container->build('log', Array) #2  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(674): Illuminate\Container\Container->make('log', Array) #3  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php(838): Illuminate\Foundation\Application->make('log') #4  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php(801): Illuminate\Container\Container->resolveClass(Object(ReflectionParameter)) #5  
/var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php(770): Illuminate\Container\Container->getDependencies(Array, Array) #6  
/var/www/mall/vendor/ in /var/www/mall/vendor/laravel/framework/src/Illuminate/Container/Container.php on line 737

大神帮忙看一下.