production.ERROR: RuntimeException: No supported encrypter found. The cipher and / or key length are invalid.

I run my laravel 5.2 app on nginx ubuntu xenial (digital ocean)

Image don't upload in my production app whereas at localhost it works fine.

In my laravel log following error is shown :

>     production.ERROR: RuntimeException: No supported encrypter found. The cipher and / or key length are invalid.in
> /var/www/laravel/bootstrap/cache/compiled.php:7771 Stack trace:
> #0 /var/www/laravel/bootstrap/cache/compiled.php(7761): Illuminate\Encryption\EncryptionServiceProvider->getEncrypterForKeyAndCipher(NULL,
> 'AES-256-CBC')

ans so on ..

How do i resolve it.

via Chebli Mohamed