Error (slack.php) : Argument #2 is not an array

[unixfox]

I set up this configuration for slack.php:

'endpoint' => 'https://chat.aresrpg.fr/hooks/xxxxx/xxxxx',

And when I do composer update it gives me an error:

> php artisan optimize --force
'endpoint' => "https://chat.aresrpg.fr/hooks/xxxxx/xxxxx",

[ErrorException]                            
array_merge(): Argument #2 is not an array        

[2016-10-05 19:14:50] production.ERROR: ErrorException: array_merge(): Argument #2 is not an array in /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Support/ServiceProvider.php:67
Stack trace:
#0 [internal function]: Illuminate\Foundation\Bootstrap\HandleExceptions->handleError(2, 'array_merge(): ...', '/usr/share/ngin...', 67, Array)
#1 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Support/ServiceProvider.php(67): array_merge(Array, 1)
#2 /usr/share/nginx/cachet/vendor/maknz/slack/src/SlackServiceProviderLaravel5.php(25): Illuminate\Support\ServiceProvider->mergeConfigFrom('/usr/share/ngin...', 'slack')
#3 /usr/share/nginx/cachet/vendor/maknz/slack/src/SlackServiceProvider.php(53): Maknz\Slack\SlackServiceProviderLaravel5->register()
#4 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(554): Maknz\Slack\SlackServiceProvider->register()
#5 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/ProviderRepository.php(74): Illuminate\Foundation\Application->register(Object(Maknz\Slack\SlackServiceProvider))
#6 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(530): Illuminate\Foundation\ProviderRepository->load(Array)
#7 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/RegisterProviders.php(17): Illuminate\Foundation\Application->registerConfiguredProviders()
#8 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(203): Illuminate\Foundation\Bootstrap\RegisterProviders->bootstrap(Object(Illuminate\Foundation\Application))
#9 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(232): Illuminate\Foundation\Application->bootstrapWith(Array)
#10 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(127): Illuminate\Foundation\Http\Kernel->bootstrap()
#11 /usr/share/nginx/cachet/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(99): Illuminate\Foundation\Http\Kernel->sendRequestThroughRouter(Object(Illuminate\Http\Request))
#12 /usr/share/nginx/cachet/public/index.php(54): Illuminate\Foundation\Http\Kernel->handle(Object(Illuminate\Http\Request))
#13 {main} {"identification":{"id":"c3a8cb31-d7fd-4231-bcfb-b909ad461c55"}} 

Does my configuration is incorrect ?

Note: The URL is correct, it's a self hosted chat service compatible with Slack.

[unixfox]

Update: I tried with:

array('https://chat.aresrpg.fr/hooks/xxxxx/xxxxx');

But doesn't work.

[unixfox]

php artisan vendor:publish copied the configuration only when I cleared cache with artisan.