laravel5.1-run PHP artisan serve times wrong

1. A sudden error occurred while running PHP artisan serve

Warning:invalid argument supplied for foreach () in D:\xampp\htdocs\baiduyun\vendor\composer\autoload_real.php on line 27Call 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:7fatal error:class ' dotenv ' not found in D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\ illuminate\foundation\bootstrap\detectenvironment.php on line 20Call 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

Reply content:

1. When I ran PHP artisan serve, I suddenly got an error.

Warning:invalid argument supplied for foreach () in D:\xampp\htdocs\baiduyun\vendor\composer\autoload_real.php on line 27Call 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:7fatal error:class ' dotenv ' not found in D:\xampp\htdocs\baiduyun\vendor\laravel\framework\src\ illuminate\foundation\bootstrap\detectenvironment.php on line 20Call 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

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