fix: use serialisation helper function (#808)

* fix: use serialisation helper function

* fix: use helper to fetch token, only close if flight client exists

graphdatascience/query_runner/gds_arrow_client.py

@@ -140,7 +140,8 @@ def request_token(self) -> Optional[str]:
             a token from the server and returns it.
         """
         if self._auth:
-            self._flight_client.authenticate_basic_token(self._auth[0], self._auth[1])
+            client = self._client()
+            client.authenticate_basic_token(self._auth[0], self._auth[1])
             return self._auth_middleware.token()
         else:
             return "IGNORED"
@@ -654,8 +655,9 @@ def _do_get(
 
         ticket = flight.Ticket(json.dumps(payload).encode("utf-8"))
 
+        client = self._client()
         try:
-            get = self._flight_client.do_get(ticket)
+            get = client.do_get(ticket)
             arrow_table = get.read_all()
         except Exception as e:
             self.handle_flight_error(e)
@@ -683,10 +685,11 @@ def __exit__(
         exception_value: Optional[BaseException],
         traceback: Optional[TracebackType],
     ) -> None:
-        self._flight_client.close()
+        self.close()
 
     def close(self) -> None:
-        self._flight_client.close()
+        if self._flight_client:
+            self._flight_client.close()
 
     def _versioned_action_type(self, action_type: str) -> str:
         return self._arrow_endpoint_version.prefix() + action_type