Fixed a Psalm issue

Author: matthewbdaly

src/AzureStorageServiceProvider.php

@@ -8,6 +8,7 @@
 use Illuminate\Support\ServiceProvider;
 use League\Flysystem\Filesystem;
 use Matthewbdaly\LaravelAzureStorage\Exceptions\EndpointNotSet;
+use Matthewbdaly\LaravelAzureStorage\Exceptions\KeyNotSet;
 use MicrosoftAzure\Storage\Blob\BlobRestProxy;
 use MicrosoftAzure\Storage\Common\Middlewares\RetryMiddleware;
 use MicrosoftAzure\Storage\Common\Middlewares\RetryMiddlewareFactory;
@@ -128,6 +129,9 @@ protected function createConnectionString(array $config): string
                 $config['sasToken']
             );
         }
+        if (!isset($config['key'])) {
+            throw new KeyNotSet();
+        }
         $endpoint = sprintf(
             'DefaultEndpointsProtocol=https;AccountName=%s;AccountKey=%s;',
             $config['name'],