Fix TypeError: WhatsApp config returns null when env vars are unset

Cast config values to string with null-coalescing fallback, and add
empty-string defaults to env() calls so instances without WhatsApp
configured still boot without TypeError.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Domain/WhatsApp/Services/WhatsAppService.php

@@ -17,9 +17,9 @@ class WhatsAppService
 
     public function __construct()
     {
-        $this->apiVersion = config('services.whatsapp.api_version', 'v25.0');
-        $this->phoneNumberId = config('services.whatsapp.phone_number_id', '');
-        $this->accessToken = config('services.whatsapp.access_token', '');
+        $this->apiVersion = (string) (config('services.whatsapp.api_version') ?? 'v25.0');
+        $this->phoneNumberId = (string) (config('services.whatsapp.phone_number_id') ?? '');
+        $this->accessToken = (string) (config('services.whatsapp.access_token') ?? '');
         $this->baseUrl = "https://graph.facebook.com/{$this->apiVersion}/{$this->phoneNumberId}";
     }
 

config/services.php

@@ -37,9 +37,9 @@
 
     'whatsapp' => [
         'api_version' => env('WHATSAPP_API_VERSION', 'v25.0'),
-        'phone_number_id' => env('WHATSAPP_PHONE_NUMBER_ID'),
-        'access_token' => env('WHATSAPP_ACCESS_TOKEN'),
-        'webhook_verify_token' => env('WHATSAPP_WEBHOOK_VERIFY_TOKEN'),
+        'phone_number_id' => env('WHATSAPP_PHONE_NUMBER_ID', ''),
+        'access_token' => env('WHATSAPP_ACCESS_TOKEN', ''),
+        'webhook_verify_token' => env('WHATSAPP_WEBHOOK_VERIFY_TOKEN', ''),
     ],
 
 ];