php artisan key:generate: ErrorException: file_get_contents(/build/src/.env): failed to open stream: No such file or directory

# php artisan key:generate

   ErrorException 

  file_get_contents(/build/src/.env): failed to open stream: No such file or directory

  at vendor/laravel/framework/src/Illuminate/Foundation/Console/KeyGenerateCommand.php:96
     92▕     {
     93▕         file_put_contents($this->laravel->environmentFilePath(), preg_replace(
     94▕             $this->keyReplacementPattern(),
     95▕             'APP_KEY='.$key,
  ➜  96▕             file_get_contents($this->laravel->environmentFilePath())
     97▕         ));
     98▕     }
     99▕ 
    100▕     /**

      +16 vendor frames 
  17  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()