use getattr to get session_id in client.py

agentops/client.py

@@ -300,7 +300,7 @@ def handle_exception(exc_type, exc_value, exc_traceback):
 
     @property
     def current_session_id(self):
-        return self._session.session_id
+        return getattr(self._session, 'session_id', None)
 
     @property
     def api_key(self):