运行php artisan serve时报错

1. 运行php artisan serve时突然就报错了

Warning: Invalid argument supplied for foreach() in D:\xampp\htdocs\baiduyun\vendor\composer\autoload_real.php on line 27

Call Stack:
    0.0012     120376   1. {main}() D:\xampp\htdocs\baiduyun\artisan:0
    0.0016     122520   2. require('D:\xampp\htdocs\baiduyun\bootstrap\autoload.php') D:\xampp\htdocs\baiduyun\artisan:16
    0.0021     123824   3. require('D:\xampp\htdocs\baiduyun\vendor\autoload.php') D:\xampp\htdocs\baiduyun\bootstrap\autoload.php:17
    0.0027     133680   4. ComposerAutoloaderInitaf5083d097d55e814d46f33a1de9d74d::getLoader() D:\xampp\htdocs\baiduyun\vendor\autoload.php:7


Fatal error: Class 'Dotenv' not found in D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\Illuminate\Foundation\Bootstrap\DetectEnvironment.php on line 20

Call Stack:
    0.0012     120376   1. {main}() D:\xampp\htdocs\baiduyun\artisan:0
    0.1532    1670160   2. Illuminate\Foundation\Console\Kernel->handle() D:\xampp\htdocs\baiduyun\artisan:36
    0.1532    1670224   3. Illuminate\Foundation\Console\Kernel->bootstrap() D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\Illuminate\Foundation\Console\Kernel.php:105
    0.1535    1670312   4. Illuminate\Foundation\Application->bootstrapWith() D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\Illuminate\Foundation\Console\Kernel.php:208
    0.1598    1675184   5. Illuminate\Foundation\Bootstrap\DetectEnvironment->bootstrap() D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\Illuminate\Foundation\Application.php:203