fix None string for webhook url and totp url

Author: wintonzheng

skyvern/forge/agent.py

@@ -187,8 +187,8 @@ async def create_task(self, task_request: TaskRequest, organization_id: str | No
         task = await app.DATABASE.create_task(
             url=str(task_request.url),
             title=task_request.title,
-            webhook_callback_url=str(task_request.webhook_callback_url),
-            totp_verification_url=str(task_request.totp_verification_url),
+            webhook_callback_url=str(task_request.webhook_callback_url) if task_request.webhook_callback_url else None,
+            totp_verification_url=str(task_request.totp_verification_url) if task_request.totp_verification_url else None,
             totp_identifier=task_request.totp_identifier,
             navigation_goal=task_request.navigation_goal,
             data_extraction_goal=task_request.data_extraction_goal,